ocfs2/dlm: Fix a race between migrate request and exit domain

[safe/jmp/linux-2.6] / fs / ocfs2 / dlm / dlmmaster.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * dlmmod.c
 *
 * standalone DLM module
 *
 * Copyright (C) 2004 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 */


#include <linux/module.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/utsname.h>
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/random.h>
#include <linux/blkdev.h>
#include <linux/socket.h>
#include <linux/inet.h>
#include <linux/spinlock.h>
#include <linux/delay.h>


#include "cluster/heartbeat.h"
#include "cluster/nodemanager.h"
#include "cluster/tcp.h"

#include "dlmapi.h"
#include "dlmcommon.h"
#include "dlmdomain.h"
#include "dlmdebug.h"

#define MLOG_MASK_PREFIX (ML_DLM|ML_DLM_MASTER)
#include "cluster/masklog.h"

static void dlm_mle_node_down(struct dlm_ctxt *dlm,
                              struct dlm_master_list_entry *mle,
                              struct o2nm_node *node,
                              int idx);
static void dlm_mle_node_up(struct dlm_ctxt *dlm,
                            struct dlm_master_list_entry *mle,
                            struct o2nm_node *node,
                            int idx);

static void dlm_assert_master_worker(struct dlm_work_item *item, void *data);
static int dlm_do_assert_master(struct dlm_ctxt *dlm,
                                struct dlm_lock_resource *res,
                                void *nodemap, u32 flags);
static void dlm_deref_lockres_worker(struct dlm_work_item *item, void *data);

static inline int dlm_mle_equal(struct dlm_ctxt *dlm,
                                struct dlm_master_list_entry *mle,
                                const char *name,
                                unsigned int namelen)
{
        struct dlm_lock_resource *res;

        if (dlm != mle->dlm)
                return 0;

        if (mle->type == DLM_MLE_BLOCK ||
            mle->type == DLM_MLE_MIGRATION) {
                if (namelen != mle->u.name.len ||
                    memcmp(name, mle->u.name.name, namelen)!=0)
                        return 0;
        } else {
                res = mle->u.res;
                if (namelen != res->lockname.len ||
                    memcmp(res->lockname.name, name, namelen) != 0)
                        return 0;
        }
        return 1;
}

static struct kmem_cache *dlm_lockres_cache = NULL;
static struct kmem_cache *dlm_lockname_cache = NULL;
static struct kmem_cache *dlm_mle_cache = NULL;

static void dlm_mle_release(struct kref *kref);
static void dlm_init_mle(struct dlm_master_list_entry *mle,
                        enum dlm_mle_type type,
                        struct dlm_ctxt *dlm,
                        struct dlm_lock_resource *res,
                        const char *name,
                        unsigned int namelen);
static void dlm_put_mle(struct dlm_master_list_entry *mle);
static void __dlm_put_mle(struct dlm_master_list_entry *mle);
static int dlm_find_mle(struct dlm_ctxt *dlm,
                        struct dlm_master_list_entry **mle,
                        char *name, unsigned int namelen);

static int dlm_do_master_request(struct dlm_lock_resource *res,
                                 struct dlm_master_list_entry *mle, int to);


static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
                                     struct dlm_lock_resource *res,
                                     struct dlm_master_list_entry *mle,
                                     int *blocked);
static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res,
                                    struct dlm_master_list_entry *mle,
                                    int blocked);
static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
                                 struct dlm_lock_resource *res,
                                 struct dlm_master_list_entry *mle,
                                 struct dlm_master_list_entry **oldmle,
                                 const char *name, unsigned int namelen,
                                 u8 new_master, u8 master);

static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res);
static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res);
static int dlm_mark_lockres_migrating(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res,
                                       u8 target);
static int dlm_pre_master_reco_lockres(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res);


int dlm_is_host_down(int errno)
{
        switch (errno) {
                case -EBADF:
                case -ECONNREFUSED:
                case -ENOTCONN:
                case -ECONNRESET:
                case -EPIPE:
                case -EHOSTDOWN:
                case -EHOSTUNREACH:
                case -ETIMEDOUT:
                case -ECONNABORTED:
                case -ENETDOWN:
                case -ENETUNREACH:
                case -ENETRESET:
                case -ESHUTDOWN:
                case -ENOPROTOOPT:
                case -EINVAL:   /* if returned from our tcp code,
                                   this means there is no socket */
                        return 1;
        }
        return 0;
}


/*
 * MASTER LIST FUNCTIONS
 */


/*
 * regarding master list entries and heartbeat callbacks:
 *
 * in order to avoid sleeping and allocation that occurs in
 * heartbeat, master list entries are simply attached to the
 * dlm's established heartbeat callbacks.  the mle is attached
 * when it is created, and since the dlm->spinlock is held at
 * that time, any heartbeat event will be properly discovered
 * by the mle.  the mle needs to be detached from the
 * dlm->mle_hb_events list as soon as heartbeat events are no
 * longer useful to the mle, and before the mle is freed.
 *
 * as a general rule, heartbeat events are no longer needed by
 * the mle once an "answer" regarding the lock master has been
 * received.
 */
static inline void __dlm_mle_attach_hb_events(struct dlm_ctxt *dlm,
                                              struct dlm_master_list_entry *mle)
{
        assert_spin_locked(&dlm->spinlock);

        list_add_tail(&mle->hb_events, &dlm->mle_hb_events);
}


static inline void __dlm_mle_detach_hb_events(struct dlm_ctxt *dlm,
                                              struct dlm_master_list_entry *mle)
{
        if (!list_empty(&mle->hb_events))
                list_del_init(&mle->hb_events);
}


static inline void dlm_mle_detach_hb_events(struct dlm_ctxt *dlm,
                                            struct dlm_master_list_entry *mle)
{
        spin_lock(&dlm->spinlock);
        __dlm_mle_detach_hb_events(dlm, mle);
        spin_unlock(&dlm->spinlock);
}

static void dlm_get_mle_inuse(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);
        mle->inuse++;
        kref_get(&mle->mle_refs);
}

static void dlm_put_mle_inuse(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        spin_lock(&dlm->spinlock);
        spin_lock(&dlm->master_lock);
        mle->inuse--;
        __dlm_put_mle(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

}

/* remove from list and free */
static void __dlm_put_mle(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);
        if (!atomic_read(&mle->mle_refs.refcount)) {
                /* this may or may not crash, but who cares.
                 * it's a BUG. */
                mlog(ML_ERROR, "bad mle: %p\n", mle);
                dlm_print_one_mle(mle);
                BUG();
        } else
                kref_put(&mle->mle_refs, dlm_mle_release);
}


/* must not have any spinlocks coming in */
static void dlm_put_mle(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        spin_lock(&dlm->spinlock);
        spin_lock(&dlm->master_lock);
        __dlm_put_mle(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);
}

static inline void dlm_get_mle(struct dlm_master_list_entry *mle)
{
        kref_get(&mle->mle_refs);
}

static void dlm_init_mle(struct dlm_master_list_entry *mle,
                        enum dlm_mle_type type,
                        struct dlm_ctxt *dlm,
                        struct dlm_lock_resource *res,
                        const char *name,
                        unsigned int namelen)
{
        assert_spin_locked(&dlm->spinlock);

        mle->dlm = dlm;
        mle->type = type;
        INIT_LIST_HEAD(&mle->list);
        INIT_LIST_HEAD(&mle->hb_events);
        memset(mle->maybe_map, 0, sizeof(mle->maybe_map));
        spin_lock_init(&mle->spinlock);
        init_waitqueue_head(&mle->wq);
        atomic_set(&mle->woken, 0);
        kref_init(&mle->mle_refs);
        memset(mle->response_map, 0, sizeof(mle->response_map));
        mle->master = O2NM_MAX_NODES;
        mle->new_master = O2NM_MAX_NODES;
        mle->inuse = 0;

        if (mle->type == DLM_MLE_MASTER) {
                BUG_ON(!res);
                mle->u.res = res;
        } else if (mle->type == DLM_MLE_BLOCK) {
                BUG_ON(!name);
                memcpy(mle->u.name.name, name, namelen);
                mle->u.name.len = namelen;
        } else /* DLM_MLE_MIGRATION */ {
                BUG_ON(!name);
                memcpy(mle->u.name.name, name, namelen);
                mle->u.name.len = namelen;
        }

        /* copy off the node_map and register hb callbacks on our copy */
        memcpy(mle->node_map, dlm->domain_map, sizeof(mle->node_map));
        memcpy(mle->vote_map, dlm->domain_map, sizeof(mle->vote_map));
        clear_bit(dlm->node_num, mle->vote_map);
        clear_bit(dlm->node_num, mle->node_map);

        /* attach the mle to the domain node up/down events */
        __dlm_mle_attach_hb_events(dlm, mle);
}


/* returns 1 if found, 0 if not */
static int dlm_find_mle(struct dlm_ctxt *dlm,
                        struct dlm_master_list_entry **mle,
                        char *name, unsigned int namelen)
{
        struct dlm_master_list_entry *tmpmle;

        assert_spin_locked(&dlm->master_lock);

        list_for_each_entry(tmpmle, &dlm->master_list, list) {
                if (!dlm_mle_equal(dlm, tmpmle, name, namelen))
                        continue;
                dlm_get_mle(tmpmle);
                *mle = tmpmle;
                return 1;
        }
        return 0;
}

void dlm_hb_event_notify_attached(struct dlm_ctxt *dlm, int idx, int node_up)
{
        struct dlm_master_list_entry *mle;

        assert_spin_locked(&dlm->spinlock);
        
        list_for_each_entry(mle, &dlm->mle_hb_events, hb_events) {
                if (node_up)
                        dlm_mle_node_up(dlm, mle, NULL, idx);
                else
                        dlm_mle_node_down(dlm, mle, NULL, idx);
        }
}

static void dlm_mle_node_down(struct dlm_ctxt *dlm,
                              struct dlm_master_list_entry *mle,
                              struct o2nm_node *node, int idx)
{
        spin_lock(&mle->spinlock);

        if (!test_bit(idx, mle->node_map))
                mlog(0, "node %u already removed from nodemap!\n", idx);
        else
                clear_bit(idx, mle->node_map);

        spin_unlock(&mle->spinlock);
}

static void dlm_mle_node_up(struct dlm_ctxt *dlm,
                            struct dlm_master_list_entry *mle,
                            struct o2nm_node *node, int idx)
{
        spin_lock(&mle->spinlock);

        if (test_bit(idx, mle->node_map))
                mlog(0, "node %u already in node map!\n", idx);
        else
                set_bit(idx, mle->node_map);

        spin_unlock(&mle->spinlock);
}


int dlm_init_mle_cache(void)
{
        dlm_mle_cache = kmem_cache_create("o2dlm_mle",
                                          sizeof(struct dlm_master_list_entry),
                                          0, SLAB_HWCACHE_ALIGN,
                                          NULL);
        if (dlm_mle_cache == NULL)
                return -ENOMEM;
        return 0;
}

void dlm_destroy_mle_cache(void)
{
        if (dlm_mle_cache)
                kmem_cache_destroy(dlm_mle_cache);
}

static void dlm_mle_release(struct kref *kref)
{
        struct dlm_master_list_entry *mle;
        struct dlm_ctxt *dlm;

        mlog_entry_void();

        mle = container_of(kref, struct dlm_master_list_entry, mle_refs);
        dlm = mle->dlm;

        if (mle->type != DLM_MLE_MASTER) {
                mlog(0, "calling mle_release for %.*s, type %d\n",
                     mle->u.name.len, mle->u.name.name, mle->type);
        } else {
                mlog(0, "calling mle_release for %.*s, type %d\n",
                     mle->u.res->lockname.len,
                     mle->u.res->lockname.name, mle->type);
        }
        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);

        /* remove from list if not already */
        if (!list_empty(&mle->list))
                list_del_init(&mle->list);

        /* detach the mle from the domain node up/down events */
        __dlm_mle_detach_hb_events(dlm, mle);

        /* NOTE: kfree under spinlock here.
         * if this is bad, we can move this to a freelist. */
        kmem_cache_free(dlm_mle_cache, mle);
}


/*
 * LOCK RESOURCE FUNCTIONS
 */

int dlm_init_master_caches(void)
{
        dlm_lockres_cache = kmem_cache_create("o2dlm_lockres",
                                              sizeof(struct dlm_lock_resource),
                                              0, SLAB_HWCACHE_ALIGN, NULL);
        if (!dlm_lockres_cache)
                goto bail;

        dlm_lockname_cache = kmem_cache_create("o2dlm_lockname",
                                               DLM_LOCKID_NAME_MAX, 0,
                                               SLAB_HWCACHE_ALIGN, NULL);
        if (!dlm_lockname_cache)
                goto bail;

        return 0;
bail:
        dlm_destroy_master_caches();
        return -ENOMEM;
}

void dlm_destroy_master_caches(void)
{
        if (dlm_lockname_cache)
                kmem_cache_destroy(dlm_lockname_cache);

        if (dlm_lockres_cache)
                kmem_cache_destroy(dlm_lockres_cache);
}

static void dlm_set_lockres_owner(struct dlm_ctxt *dlm,
                                  struct dlm_lock_resource *res,
                                  u8 owner)
{
        assert_spin_locked(&res->spinlock);

        mlog_entry("%.*s, %u\n", res->lockname.len, res->lockname.name, owner);

        if (owner == dlm->node_num)
                atomic_inc(&dlm->local_resources);
        else if (owner == DLM_LOCK_RES_OWNER_UNKNOWN)
                atomic_inc(&dlm->unknown_resources);
        else
                atomic_inc(&dlm->remote_resources);

        res->owner = owner;
}

void dlm_change_lockres_owner(struct dlm_ctxt *dlm,
                              struct dlm_lock_resource *res, u8 owner)
{
        assert_spin_locked(&res->spinlock);

        if (owner == res->owner)
                return;

        if (res->owner == dlm->node_num)
                atomic_dec(&dlm->local_resources);
        else if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN)
                atomic_dec(&dlm->unknown_resources);
        else
                atomic_dec(&dlm->remote_resources);

        dlm_set_lockres_owner(dlm, res, owner);
}


static void dlm_lockres_release(struct kref *kref)
{
        struct dlm_lock_resource *res;

        res = container_of(kref, struct dlm_lock_resource, refs);

        /* This should not happen -- all lockres' have a name
         * associated with them at init time. */
        BUG_ON(!res->lockname.name);

        mlog(0, "destroying lockres %.*s\n", res->lockname.len,
             res->lockname.name);

        if (!list_empty(&res->tracking))
                list_del_init(&res->tracking);
        else {
                mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
                     res->lockname.len, res->lockname.name);
                dlm_print_one_lock_resource(res);
        }

        if (!hlist_unhashed(&res->hash_node) ||
            !list_empty(&res->granted) ||
            !list_empty(&res->converting) ||
            !list_empty(&res->blocked) ||
            !list_empty(&res->dirty) ||
            !list_empty(&res->recovering) ||
            !list_empty(&res->purge)) {
                mlog(ML_ERROR,
                     "Going to BUG for resource %.*s."
                     "  We're on a list! [%c%c%c%c%c%c%c]\n",
                     res->lockname.len, res->lockname.name,
                     !hlist_unhashed(&res->hash_node) ? 'H' : ' ',
                     !list_empty(&res->granted) ? 'G' : ' ',
                     !list_empty(&res->converting) ? 'C' : ' ',
                     !list_empty(&res->blocked) ? 'B' : ' ',
                     !list_empty(&res->dirty) ? 'D' : ' ',
                     !list_empty(&res->recovering) ? 'R' : ' ',
                     !list_empty(&res->purge) ? 'P' : ' ');

                dlm_print_one_lock_resource(res);
        }

        /* By the time we're ready to blow this guy away, we shouldn't
         * be on any lists. */
        BUG_ON(!hlist_unhashed(&res->hash_node));
        BUG_ON(!list_empty(&res->granted));
        BUG_ON(!list_empty(&res->converting));
        BUG_ON(!list_empty(&res->blocked));
        BUG_ON(!list_empty(&res->dirty));
        BUG_ON(!list_empty(&res->recovering));
        BUG_ON(!list_empty(&res->purge));

        kmem_cache_free(dlm_lockname_cache, (void *)res->lockname.name);

        kmem_cache_free(dlm_lockres_cache, res);
}

void dlm_lockres_put(struct dlm_lock_resource *res)
{
        kref_put(&res->refs, dlm_lockres_release);
}

static void dlm_init_lockres(struct dlm_ctxt *dlm,
                             struct dlm_lock_resource *res,
                             const char *name, unsigned int namelen)
{
        char *qname;

        /* If we memset here, we lose our reference to the kmalloc'd
         * res->lockname.name, so be sure to init every field
         * correctly! */

        qname = (char *) res->lockname.name;
        memcpy(qname, name, namelen);

        res->lockname.len = namelen;
        res->lockname.hash = dlm_lockid_hash(name, namelen);

        init_waitqueue_head(&res->wq);
        spin_lock_init(&res->spinlock);
        INIT_HLIST_NODE(&res->hash_node);
        INIT_LIST_HEAD(&res->granted);
        INIT_LIST_HEAD(&res->converting);
        INIT_LIST_HEAD(&res->blocked);
        INIT_LIST_HEAD(&res->dirty);
        INIT_LIST_HEAD(&res->recovering);
        INIT_LIST_HEAD(&res->purge);
        INIT_LIST_HEAD(&res->tracking);
        atomic_set(&res->asts_reserved, 0);
        res->migration_pending = 0;
        res->inflight_locks = 0;

        kref_init(&res->refs);

        /* just for consistency */
        spin_lock(&res->spinlock);
        dlm_set_lockres_owner(dlm, res, DLM_LOCK_RES_OWNER_UNKNOWN);
        spin_unlock(&res->spinlock);

        res->state = DLM_LOCK_RES_IN_PROGRESS;

        res->last_used = 0;

        spin_lock(&dlm->spinlock);
        list_add_tail(&res->tracking, &dlm->tracking_list);
        spin_unlock(&dlm->spinlock);

        memset(res->lvb, 0, DLM_LVB_LEN);
        memset(res->refmap, 0, sizeof(res->refmap));
}

struct dlm_lock_resource *dlm_new_lockres(struct dlm_ctxt *dlm,
                                   const char *name,
                                   unsigned int namelen)
{
        struct dlm_lock_resource *res = NULL;

        res = (struct dlm_lock_resource *)
                                kmem_cache_zalloc(dlm_lockres_cache, GFP_NOFS);
        if (!res)
                goto error;

        res->lockname.name = (char *)
                                kmem_cache_zalloc(dlm_lockname_cache, GFP_NOFS);
        if (!res->lockname.name)
                goto error;

        dlm_init_lockres(dlm, res, name, namelen);
        return res;

error:
        if (res && res->lockname.name)
                kmem_cache_free(dlm_lockname_cache, (void *)res->lockname.name);

        if (res)
                kmem_cache_free(dlm_lockres_cache, res);
        return NULL;
}

void __dlm_lockres_grab_inflight_ref(struct dlm_ctxt *dlm,
                                   struct dlm_lock_resource *res,
                                   int new_lockres,
                                   const char *file,
                                   int line)
{
        if (!new_lockres)
                assert_spin_locked(&res->spinlock);

        if (!test_bit(dlm->node_num, res->refmap)) {
                BUG_ON(res->inflight_locks != 0);
                dlm_lockres_set_refmap_bit(dlm->node_num, res);
        }
        res->inflight_locks++;
        mlog(0, "%s:%.*s: inflight++: now %u\n",
             dlm->name, res->lockname.len, res->lockname.name,
             res->inflight_locks);
}

void __dlm_lockres_drop_inflight_ref(struct dlm_ctxt *dlm,
                                   struct dlm_lock_resource *res,
                                   const char *file,
                                   int line)
{
        assert_spin_locked(&res->spinlock);

        BUG_ON(res->inflight_locks == 0);
        res->inflight_locks--;
        mlog(0, "%s:%.*s: inflight--: now %u\n",
             dlm->name, res->lockname.len, res->lockname.name,
             res->inflight_locks);
        if (res->inflight_locks == 0)
                dlm_lockres_clear_refmap_bit(dlm->node_num, res);
        wake_up(&res->wq);
}

/*
 * lookup a lock resource by name.
 * may already exist in the hashtable.
 * lockid is null terminated
 *
 * if not, allocate enough for the lockres and for
 * the temporary structure used in doing the mastering.
 *
 * also, do a lookup in the dlm->master_list to see
 * if another node has begun mastering the same lock.
 * if so, there should be a block entry in there
 * for this name, and we should *not* attempt to master
 * the lock here.   need to wait around for that node
 * to assert_master (or die).
 *
 */
struct dlm_lock_resource * dlm_get_lock_resource(struct dlm_ctxt *dlm,
                                          const char *lockid,
                                          int namelen,
                                          int flags)
{
        struct dlm_lock_resource *tmpres=NULL, *res=NULL;
        struct dlm_master_list_entry *mle = NULL;
        struct dlm_master_list_entry *alloc_mle = NULL;
        int blocked = 0;
        int ret, nodenum;
        struct dlm_node_iter iter;
        unsigned int hash;
        int tries = 0;
        int bit, wait_on_recovery = 0;
        int drop_inflight_if_nonlocal = 0;

        BUG_ON(!lockid);

        hash = dlm_lockid_hash(lockid, namelen);

        mlog(0, "get lockres %s (len %d)\n", lockid, namelen);

lookup:
        spin_lock(&dlm->spinlock);
        tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
        if (tmpres) {
                int dropping_ref = 0;

                spin_lock(&tmpres->spinlock);
                if (tmpres->owner == dlm->node_num) {
                        BUG_ON(tmpres->state & DLM_LOCK_RES_DROPPING_REF);
                        dlm_lockres_grab_inflight_ref(dlm, tmpres);
                } else if (tmpres->state & DLM_LOCK_RES_DROPPING_REF)
                        dropping_ref = 1;
                spin_unlock(&tmpres->spinlock);
                spin_unlock(&dlm->spinlock);

                /* wait until done messaging the master, drop our ref to allow
                 * the lockres to be purged, start over. */
                if (dropping_ref) {
                        spin_lock(&tmpres->spinlock);
                        __dlm_wait_on_lockres_flags(tmpres, DLM_LOCK_RES_DROPPING_REF);
                        spin_unlock(&tmpres->spinlock);
                        dlm_lockres_put(tmpres);
                        tmpres = NULL;
                        goto lookup;
                }

                mlog(0, "found in hash!\n");
                if (res)
                        dlm_lockres_put(res);
                res = tmpres;
                goto leave;
        }

        if (!res) {
                spin_unlock(&dlm->spinlock);
                mlog(0, "allocating a new resource\n");
                /* nothing found and we need to allocate one. */
                alloc_mle = (struct dlm_master_list_entry *)
                        kmem_cache_alloc(dlm_mle_cache, GFP_NOFS);
                if (!alloc_mle)
                        goto leave;
                res = dlm_new_lockres(dlm, lockid, namelen);
                if (!res)
                        goto leave;
                goto lookup;
        }

        mlog(0, "no lockres found, allocated our own: %p\n", res);

        if (flags & LKM_LOCAL) {
                /* caller knows it's safe to assume it's not mastered elsewhere
                 * DONE!  return right away */
                spin_lock(&res->spinlock);
                dlm_change_lockres_owner(dlm, res, dlm->node_num);
                __dlm_insert_lockres(dlm, res);
                dlm_lockres_grab_inflight_ref(dlm, res);
                spin_unlock(&res->spinlock);
                spin_unlock(&dlm->spinlock);
                /* lockres still marked IN_PROGRESS */
                goto wake_waiters;
        }

        /* check master list to see if another node has started mastering it */
        spin_lock(&dlm->master_lock);

        /* if we found a block, wait for lock to be mastered by another node */
        blocked = dlm_find_mle(dlm, &mle, (char *)lockid, namelen);
        if (blocked) {
                int mig;
                if (mle->type == DLM_MLE_MASTER) {
                        mlog(ML_ERROR, "master entry for nonexistent lock!\n");
                        BUG();
                }
                mig = (mle->type == DLM_MLE_MIGRATION);
                /* if there is a migration in progress, let the migration
                 * finish before continuing.  we can wait for the absence
                 * of the MIGRATION mle: either the migrate finished or
                 * one of the nodes died and the mle was cleaned up.
                 * if there is a BLOCK here, but it already has a master
                 * set, we are too late.  the master does not have a ref
                 * for us in the refmap.  detach the mle and drop it.
                 * either way, go back to the top and start over. */
                if (mig || mle->master != O2NM_MAX_NODES) {
                        BUG_ON(mig && mle->master == dlm->node_num);
                        /* we arrived too late.  the master does not
                         * have a ref for us. retry. */
                        mlog(0, "%s:%.*s: late on %s\n",
                             dlm->name, namelen, lockid,
                             mig ?  "MIGRATION" : "BLOCK");
                        spin_unlock(&dlm->master_lock);
                        spin_unlock(&dlm->spinlock);

                        /* master is known, detach */
                        if (!mig)
                                dlm_mle_detach_hb_events(dlm, mle);
                        dlm_put_mle(mle);
                        mle = NULL;
                        /* this is lame, but we cant wait on either
                         * the mle or lockres waitqueue here */
                        if (mig)
                                msleep(100);
                        goto lookup;
                }
        } else {
                /* go ahead and try to master lock on this node */
                mle = alloc_mle;
                /* make sure this does not get freed below */
                alloc_mle = NULL;
                dlm_init_mle(mle, DLM_MLE_MASTER, dlm, res, NULL, 0);
                set_bit(dlm->node_num, mle->maybe_map);
                list_add(&mle->list, &dlm->master_list);

                /* still holding the dlm spinlock, check the recovery map
                 * to see if there are any nodes that still need to be 
                 * considered.  these will not appear in the mle nodemap
                 * but they might own this lockres.  wait on them. */
                bit = find_next_bit(dlm->recovery_map, O2NM_MAX_NODES, 0);
                if (bit < O2NM_MAX_NODES) {
                        mlog(ML_NOTICE, "%s:%.*s: at least one node (%d) to "
                             "recover before lock mastery can begin\n",
                             dlm->name, namelen, (char *)lockid, bit);
                        wait_on_recovery = 1;
                }
        }

        /* at this point there is either a DLM_MLE_BLOCK or a
         * DLM_MLE_MASTER on the master list, so it's safe to add the
         * lockres to the hashtable.  anyone who finds the lock will
         * still have to wait on the IN_PROGRESS. */

        /* finally add the lockres to its hash bucket */
        __dlm_insert_lockres(dlm, res);
        /* since this lockres is new it doesnt not require the spinlock */
        dlm_lockres_grab_inflight_ref_new(dlm, res);

        /* if this node does not become the master make sure to drop
         * this inflight reference below */
        drop_inflight_if_nonlocal = 1;

        /* get an extra ref on the mle in case this is a BLOCK
         * if so, the creator of the BLOCK may try to put the last
         * ref at this time in the assert master handler, so we
         * need an extra one to keep from a bad ptr deref. */
        dlm_get_mle_inuse(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

redo_request:
        while (wait_on_recovery) {
                /* any cluster changes that occurred after dropping the
                 * dlm spinlock would be detectable be a change on the mle,
                 * so we only need to clear out the recovery map once. */
                if (dlm_is_recovery_lock(lockid, namelen)) {
                        mlog(ML_NOTICE, "%s: recovery map is not empty, but "
                             "must master $RECOVERY lock now\n", dlm->name);
                        if (!dlm_pre_master_reco_lockres(dlm, res))
                                wait_on_recovery = 0;
                        else {
                                mlog(0, "%s: waiting 500ms for heartbeat state "
                                    "change\n", dlm->name);
                                msleep(500);
                        }
                        continue;
                } 

                dlm_kick_recovery_thread(dlm);
                msleep(1000);
                dlm_wait_for_recovery(dlm);

                spin_lock(&dlm->spinlock);
                bit = find_next_bit(dlm->recovery_map, O2NM_MAX_NODES, 0);
                if (bit < O2NM_MAX_NODES) {
                        mlog(ML_NOTICE, "%s:%.*s: at least one node (%d) to "
                             "recover before lock mastery can begin\n",
                             dlm->name, namelen, (char *)lockid, bit);
                        wait_on_recovery = 1;
                } else
                        wait_on_recovery = 0;
                spin_unlock(&dlm->spinlock);

                if (wait_on_recovery)
                        dlm_wait_for_node_recovery(dlm, bit, 10000);
        }

        /* must wait for lock to be mastered elsewhere */
        if (blocked)
                goto wait;

        ret = -EINVAL;
        dlm_node_iter_init(mle->vote_map, &iter);
        while ((nodenum = dlm_node_iter_next(&iter)) >= 0) {
                ret = dlm_do_master_request(res, mle, nodenum);
                if (ret < 0)
                        mlog_errno(ret);
                if (mle->master != O2NM_MAX_NODES) {
                        /* found a master ! */
                        if (mle->master <= nodenum)
                                break;
                        /* if our master request has not reached the master
                         * yet, keep going until it does.  this is how the
                         * master will know that asserts are needed back to
                         * the lower nodes. */
                        mlog(0, "%s:%.*s: requests only up to %u but master "
                             "is %u, keep going\n", dlm->name, namelen,
                             lockid, nodenum, mle->master);
                }
        }

wait:
        /* keep going until the response map includes all nodes */
        ret = dlm_wait_for_lock_mastery(dlm, res, mle, &blocked);
        if (ret < 0) {
                wait_on_recovery = 1;
                mlog(0, "%s:%.*s: node map changed, redo the "
                     "master request now, blocked=%d\n",
                     dlm->name, res->lockname.len,
                     res->lockname.name, blocked);
                if (++tries > 20) {
                        mlog(ML_ERROR, "%s:%.*s: spinning on "
                             "dlm_wait_for_lock_mastery, blocked=%d\n", 
                             dlm->name, res->lockname.len, 
                             res->lockname.name, blocked);
                        dlm_print_one_lock_resource(res);
                        dlm_print_one_mle(mle);
                        tries = 0;
                }
                goto redo_request;
        }

        mlog(0, "lockres mastered by %u\n", res->owner);
        /* make sure we never continue without this */
        BUG_ON(res->owner == O2NM_MAX_NODES);

        /* master is known, detach if not already detached */
        dlm_mle_detach_hb_events(dlm, mle);
        dlm_put_mle(mle);
        /* put the extra ref */
        dlm_put_mle_inuse(mle);

wake_waiters:
        spin_lock(&res->spinlock);
        if (res->owner != dlm->node_num && drop_inflight_if_nonlocal)
                dlm_lockres_drop_inflight_ref(dlm, res);
        res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);

leave:
        /* need to free the unused mle */
        if (alloc_mle)
                kmem_cache_free(dlm_mle_cache, alloc_mle);

        return res;
}


#define DLM_MASTERY_TIMEOUT_MS   5000

static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
                                     struct dlm_lock_resource *res,
                                     struct dlm_master_list_entry *mle,
                                     int *blocked)
{
        u8 m;
        int ret, bit;
        int map_changed, voting_done;
        int assert, sleep;

recheck:
        ret = 0;
        assert = 0;

        /* check if another node has already become the owner */
        spin_lock(&res->spinlock);
        if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
                mlog(0, "%s:%.*s: owner is suddenly %u\n", dlm->name,
                     res->lockname.len, res->lockname.name, res->owner);
                spin_unlock(&res->spinlock);
                /* this will cause the master to re-assert across
                 * the whole cluster, freeing up mles */
                if (res->owner != dlm->node_num) {
                        ret = dlm_do_master_request(res, mle, res->owner);
                        if (ret < 0) {
                                /* give recovery a chance to run */
                                mlog(ML_ERROR, "link to %u went down?: %d\n", res->owner, ret);
                                msleep(500);
                                goto recheck;
                        }
                }
                ret = 0;
                goto leave;
        }
        spin_unlock(&res->spinlock);

        spin_lock(&mle->spinlock);
        m = mle->master;
        map_changed = (memcmp(mle->vote_map, mle->node_map,
                              sizeof(mle->vote_map)) != 0);
        voting_done = (memcmp(mle->vote_map, mle->response_map,
                             sizeof(mle->vote_map)) == 0);

        /* restart if we hit any errors */
        if (map_changed) {
                int b;
                mlog(0, "%s: %.*s: node map changed, restarting\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                ret = dlm_restart_lock_mastery(dlm, res, mle, *blocked);
                b = (mle->type == DLM_MLE_BLOCK);
                if ((*blocked && !b) || (!*blocked && b)) {
                        mlog(0, "%s:%.*s: status change: old=%d new=%d\n", 
                             dlm->name, res->lockname.len, res->lockname.name,
                             *blocked, b);
                        *blocked = b;
                }
                spin_unlock(&mle->spinlock);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto leave;
                }
                mlog(0, "%s:%.*s: restart lock mastery succeeded, "
                     "rechecking now\n", dlm->name, res->lockname.len,
                     res->lockname.name);
                goto recheck;
        } else {
                if (!voting_done) {
                        mlog(0, "map not changed and voting not done "
                             "for %s:%.*s\n", dlm->name, res->lockname.len,
                             res->lockname.name);
                }
        }

        if (m != O2NM_MAX_NODES) {
                /* another node has done an assert!
                 * all done! */
                sleep = 0;
        } else {
                sleep = 1;
                /* have all nodes responded? */
                if (voting_done && !*blocked) {
                        bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
                        if (dlm->node_num <= bit) {
                                /* my node number is lowest.
                                 * now tell other nodes that I am
                                 * mastering this. */
                                mle->master = dlm->node_num;
                                /* ref was grabbed in get_lock_resource
                                 * will be dropped in dlmlock_master */
                                assert = 1;
                                sleep = 0;
                        }
                        /* if voting is done, but we have not received
                         * an assert master yet, we must sleep */
                }
        }

        spin_unlock(&mle->spinlock);

        /* sleep if we haven't finished voting yet */
        if (sleep) {
                unsigned long timeo = msecs_to_jiffies(DLM_MASTERY_TIMEOUT_MS);

                /*
                if (atomic_read(&mle->mle_refs.refcount) < 2)
                        mlog(ML_ERROR, "mle (%p) refs=%d, name=%.*s\n", mle,
                        atomic_read(&mle->mle_refs.refcount),
                        res->lockname.len, res->lockname.name);
                */
                atomic_set(&mle->woken, 0);
                (void)wait_event_timeout(mle->wq,
                                         (atomic_read(&mle->woken) == 1),
                                         timeo);
                if (res->owner == O2NM_MAX_NODES) {
                        mlog(0, "%s:%.*s: waiting again\n", dlm->name,
                             res->lockname.len, res->lockname.name);
                        goto recheck;
                }
                mlog(0, "done waiting, master is %u\n", res->owner);
                ret = 0;
                goto leave;
        }

        ret = 0;   /* done */
        if (assert) {
                m = dlm->node_num;
                mlog(0, "about to master %.*s here, this=%u\n",
                     res->lockname.len, res->lockname.name, m);
                ret = dlm_do_assert_master(dlm, res, mle->vote_map, 0);
                if (ret) {
                        /* This is a failure in the network path,
                         * not in the response to the assert_master
                         * (any nonzero response is a BUG on this node).
                         * Most likely a socket just got disconnected
                         * due to node death. */
                        mlog_errno(ret);
                }
                /* no longer need to restart lock mastery.
                 * all living nodes have been contacted. */
                ret = 0;
        }

        /* set the lockres owner */
        spin_lock(&res->spinlock);
        /* mastery reference obtained either during
         * assert_master_handler or in get_lock_resource */
        dlm_change_lockres_owner(dlm, res, m);
        spin_unlock(&res->spinlock);

leave:
        return ret;
}

struct dlm_bitmap_diff_iter
{
        int curnode;
        unsigned long *orig_bm;
        unsigned long *cur_bm;
        unsigned long diff_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
};

enum dlm_node_state_change
{
        NODE_DOWN = -1,
        NODE_NO_CHANGE = 0,
        NODE_UP
};

static void dlm_bitmap_diff_iter_init(struct dlm_bitmap_diff_iter *iter,
                                      unsigned long *orig_bm,
                                      unsigned long *cur_bm)
{
        unsigned long p1, p2;
        int i;

        iter->curnode = -1;
        iter->orig_bm = orig_bm;
        iter->cur_bm = cur_bm;

        for (i = 0; i < BITS_TO_LONGS(O2NM_MAX_NODES); i++) {
                p1 = *(iter->orig_bm + i);
                p2 = *(iter->cur_bm + i);
                iter->diff_bm[i] = (p1 & ~p2) | (p2 & ~p1);
        }
}

static int dlm_bitmap_diff_iter_next(struct dlm_bitmap_diff_iter *iter,
                                     enum dlm_node_state_change *state)
{
        int bit;

        if (iter->curnode >= O2NM_MAX_NODES)
                return -ENOENT;

        bit = find_next_bit(iter->diff_bm, O2NM_MAX_NODES,
                            iter->curnode+1);
        if (bit >= O2NM_MAX_NODES) {
                iter->curnode = O2NM_MAX_NODES;
                return -ENOENT;
        }

        /* if it was there in the original then this node died */
        if (test_bit(bit, iter->orig_bm))
                *state = NODE_DOWN;
        else
                *state = NODE_UP;

        iter->curnode = bit;
        return bit;
}


static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res,
                                    struct dlm_master_list_entry *mle,
                                    int blocked)
{
        struct dlm_bitmap_diff_iter bdi;
        enum dlm_node_state_change sc;
        int node;
        int ret = 0;

        mlog(0, "something happened such that the "
             "master process may need to be restarted!\n");

        assert_spin_locked(&mle->spinlock);

        dlm_bitmap_diff_iter_init(&bdi, mle->vote_map, mle->node_map);
        node = dlm_bitmap_diff_iter_next(&bdi, &sc);
        while (node >= 0) {
                if (sc == NODE_UP) {
                        /* a node came up.  clear any old vote from
                         * the response map and set it in the vote map
                         * then restart the mastery. */
                        mlog(ML_NOTICE, "node %d up while restarting\n", node);

                        /* redo the master request, but only for the new node */
                        mlog(0, "sending request to new node\n");
                        clear_bit(node, mle->response_map);
                        set_bit(node, mle->vote_map);
                } else {
                        mlog(ML_ERROR, "node down! %d\n", node);
                        if (blocked) {
                                int lowest = find_next_bit(mle->maybe_map,
                                                       O2NM_MAX_NODES, 0);

                                /* act like it was never there */
                                clear_bit(node, mle->maybe_map);

                                if (node == lowest) {
                                        mlog(0, "expected master %u died"
                                            " while this node was blocked "
                                            "waiting on it!\n", node);
                                        lowest = find_next_bit(mle->maybe_map,
                                                        O2NM_MAX_NODES,
                                                        lowest+1);
                                        if (lowest < O2NM_MAX_NODES) {
                                                mlog(0, "%s:%.*s:still "
                                                     "blocked. waiting on %u "
                                                     "now\n", dlm->name,
                                                     res->lockname.len,
                                                     res->lockname.name,
                                                     lowest);
                                        } else {
                                                /* mle is an MLE_BLOCK, but
                                                 * there is now nothing left to
                                                 * block on.  we need to return
                                                 * all the way back out and try
                                                 * again with an MLE_MASTER.
                                                 * dlm_do_local_recovery_cleanup
                                                 * has already run, so the mle
                                                 * refcount is ok */
                                                mlog(0, "%s:%.*s: no "
                                                     "longer blocking. try to "
                                                     "master this here\n",
                                                     dlm->name,
                                                     res->lockname.len,
                                                     res->lockname.name);
                                                mle->type = DLM_MLE_MASTER;
                                                mle->u.res = res;
                                        }
                                }
                        }

                        /* now blank out everything, as if we had never
                         * contacted anyone */
                        memset(mle->maybe_map, 0, sizeof(mle->maybe_map));
                        memset(mle->response_map, 0, sizeof(mle->response_map));
                        /* reset the vote_map to the current node_map */
                        memcpy(mle->vote_map, mle->node_map,
                               sizeof(mle->node_map));
                        /* put myself into the maybe map */
                        if (mle->type != DLM_MLE_BLOCK)
                                set_bit(dlm->node_num, mle->maybe_map);
                }
                ret = -EAGAIN;
                node = dlm_bitmap_diff_iter_next(&bdi, &sc);
        }
        return ret;
}


/*
 * DLM_MASTER_REQUEST_MSG
 *
 * returns: 0 on success,
 *          -errno on a network error
 *
 * on error, the caller should assume the target node is "dead"
 *
 */

static int dlm_do_master_request(struct dlm_lock_resource *res,
                                 struct dlm_master_list_entry *mle, int to)
{
        struct dlm_ctxt *dlm = mle->dlm;
        struct dlm_master_request request;
        int ret, response=0, resend;

        memset(&request, 0, sizeof(request));
        request.node_idx = dlm->node_num;

        BUG_ON(mle->type == DLM_MLE_MIGRATION);

        if (mle->type != DLM_MLE_MASTER) {
                request.namelen = mle->u.name.len;
                memcpy(request.name, mle->u.name.name, request.namelen);
        } else {
                request.namelen = mle->u.res->lockname.len;
                memcpy(request.name, mle->u.res->lockname.name,
                        request.namelen);
        }

again:
        ret = o2net_send_message(DLM_MASTER_REQUEST_MSG, dlm->key, &request,
                                 sizeof(request), to, &response);
        if (ret < 0)  {
                if (ret == -ESRCH) {
                        /* should never happen */
                        mlog(ML_ERROR, "TCP stack not ready!\n");
                        BUG();
                } else if (ret == -EINVAL) {
                        mlog(ML_ERROR, "bad args passed to o2net!\n");
                        BUG();
                } else if (ret == -ENOMEM) {
                        mlog(ML_ERROR, "out of memory while trying to send "
                             "network message!  retrying\n");
                        /* this is totally crude */
                        msleep(50);
                        goto again;
                } else if (!dlm_is_host_down(ret)) {
                        /* not a network error. bad. */
                        mlog_errno(ret);
                        mlog(ML_ERROR, "unhandled error!");
                        BUG();
                }
                /* all other errors should be network errors,
                 * and likely indicate node death */
                mlog(ML_ERROR, "link to %d went down!\n", to);
                goto out;
        }

        ret = 0;
        resend = 0;
        spin_lock(&mle->spinlock);
        switch (response) {
                case DLM_MASTER_RESP_YES:
                        set_bit(to, mle->response_map);
                        mlog(0, "node %u is the master, response=YES\n", to);
                        mlog(0, "%s:%.*s: master node %u now knows I have a "
                             "reference\n", dlm->name, res->lockname.len,
                             res->lockname.name, to);
                        mle->master = to;
                        break;
                case DLM_MASTER_RESP_NO:
                        mlog(0, "node %u not master, response=NO\n", to);
                        set_bit(to, mle->response_map);
                        break;
                case DLM_MASTER_RESP_MAYBE:
                        mlog(0, "node %u not master, response=MAYBE\n", to);
                        set_bit(to, mle->response_map);
                        set_bit(to, mle->maybe_map);
                        break;
                case DLM_MASTER_RESP_ERROR:
                        mlog(0, "node %u hit an error, resending\n", to);
                        resend = 1;
                        response = 0;
                        break;
                default:
                        mlog(ML_ERROR, "bad response! %u\n", response);
                        BUG();
        }
        spin_unlock(&mle->spinlock);
        if (resend) {
                /* this is also totally crude */
                msleep(50);
                goto again;
        }

out:
        return ret;
}

/*
 * locks that can be taken here:
 * dlm->spinlock
 * res->spinlock
 * mle->spinlock
 * dlm->master_list
 *
 * if possible, TRIM THIS DOWN!!!
 */
int dlm_master_request_handler(struct o2net_msg *msg, u32 len, void *data,
                               void **ret_data)
{
        u8 response = DLM_MASTER_RESP_MAYBE;
        struct dlm_ctxt *dlm = data;
        struct dlm_lock_resource *res = NULL;
        struct dlm_master_request *request = (struct dlm_master_request *) msg->buf;
        struct dlm_master_list_entry *mle = NULL, *tmpmle = NULL;
        char *name;
        unsigned int namelen, hash;
        int found, ret;
        int set_maybe;
        int dispatch_assert = 0;

        if (!dlm_grab(dlm))
                return DLM_MASTER_RESP_NO;

        if (!dlm_domain_fully_joined(dlm)) {
                response = DLM_MASTER_RESP_NO;
                goto send_response;
        }

        name = request->name;
        namelen = request->namelen;
        hash = dlm_lockid_hash(name, namelen);

        if (namelen > DLM_LOCKID_NAME_MAX) {
                response = DLM_IVBUFLEN;
                goto send_response;
        }

way_up_top:
        spin_lock(&dlm->spinlock);
        res = __dlm_lookup_lockres(dlm, name, namelen, hash);
        if (res) {
                spin_unlock(&dlm->spinlock);

                /* take care of the easy cases up front */
                spin_lock(&res->spinlock);
                if (res->state & (DLM_LOCK_RES_RECOVERING|
                                  DLM_LOCK_RES_MIGRATING)) {
                        spin_unlock(&res->spinlock);
                        mlog(0, "returning DLM_MASTER_RESP_ERROR since res is "
                             "being recovered/migrated\n");
                        response = DLM_MASTER_RESP_ERROR;
                        if (mle)
                                kmem_cache_free(dlm_mle_cache, mle);
                        goto send_response;
                }

                if (res->owner == dlm->node_num) {
                        mlog(0, "%s:%.*s: setting bit %u in refmap\n",
                             dlm->name, namelen, name, request->node_idx);
                        dlm_lockres_set_refmap_bit(request->node_idx, res);
                        spin_unlock(&res->spinlock);
                        response = DLM_MASTER_RESP_YES;
                        if (mle)
                                kmem_cache_free(dlm_mle_cache, mle);

                        /* this node is the owner.
                         * there is some extra work that needs to
                         * happen now.  the requesting node has
                         * caused all nodes up to this one to
                         * create mles.  this node now needs to
                         * go back and clean those up. */
                        dispatch_assert = 1;
                        goto send_response;
                } else if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
                        spin_unlock(&res->spinlock);
                        // mlog(0, "node %u is the master\n", res->owner);
                        response = DLM_MASTER_RESP_NO;
                        if (mle)
                                kmem_cache_free(dlm_mle_cache, mle);
                        goto send_response;
                }

                /* ok, there is no owner.  either this node is
                 * being blocked, or it is actively trying to
                 * master this lock. */
                if (!(res->state & DLM_LOCK_RES_IN_PROGRESS)) {
                        mlog(ML_ERROR, "lock with no owner should be "
                             "in-progress!\n");
                        BUG();
                }

                // mlog(0, "lockres is in progress...\n");
                spin_lock(&dlm->master_lock);
                found = dlm_find_mle(dlm, &tmpmle, name, namelen);
                if (!found) {
                        mlog(ML_ERROR, "no mle found for this lock!\n");
                        BUG();
                }
                set_maybe = 1;
                spin_lock(&tmpmle->spinlock);
                if (tmpmle->type == DLM_MLE_BLOCK) {
                        // mlog(0, "this node is waiting for "
                        // "lockres to be mastered\n");
                        response = DLM_MASTER_RESP_NO;
                } else if (tmpmle->type == DLM_MLE_MIGRATION) {
                        mlog(0, "node %u is master, but trying to migrate to "
                             "node %u.\n", tmpmle->master, tmpmle->new_master);
                        if (tmpmle->master == dlm->node_num) {
                                mlog(ML_ERROR, "no owner on lockres, but this "
                                     "node is trying to migrate it to %u?!\n",
                                     tmpmle->new_master);
                                BUG();
                        } else {
                                /* the real master can respond on its own */
                                response = DLM_MASTER_RESP_NO;
                        }
                } else if (tmpmle->master != DLM_LOCK_RES_OWNER_UNKNOWN) {
                        set_maybe = 0;
                        if (tmpmle->master == dlm->node_num) {
                                response = DLM_MASTER_RESP_YES;
                                /* this node will be the owner.
                                 * go back and clean the mles on any
                                 * other nodes */
                                dispatch_assert = 1;
                                dlm_lockres_set_refmap_bit(request->node_idx, res);
                                mlog(0, "%s:%.*s: setting bit %u in refmap\n",
                                     dlm->name, namelen, name,
                                     request->node_idx);
                        } else
                                response = DLM_MASTER_RESP_NO;
                } else {
                        // mlog(0, "this node is attempting to "
                        // "master lockres\n");
                        response = DLM_MASTER_RESP_MAYBE;
                }
                if (set_maybe)
                        set_bit(request->node_idx, tmpmle->maybe_map);
                spin_unlock(&tmpmle->spinlock);

                spin_unlock(&dlm->master_lock);
                spin_unlock(&res->spinlock);

                /* keep the mle attached to heartbeat events */
                dlm_put_mle(tmpmle);
                if (mle)
                        kmem_cache_free(dlm_mle_cache, mle);
                goto send_response;
        }

        /*
         * lockres doesn't exist on this node
         * if there is an MLE_BLOCK, return NO
         * if there is an MLE_MASTER, return MAYBE
         * otherwise, add an MLE_BLOCK, return NO
         */
        spin_lock(&dlm->master_lock);
        found = dlm_find_mle(dlm, &tmpmle, name, namelen);
        if (!found) {
                /* this lockid has never been seen on this node yet */
                // mlog(0, "no mle found\n");
                if (!mle) {
                        spin_unlock(&dlm->master_lock);
                        spin_unlock(&dlm->spinlock);

                        mle = (struct dlm_master_list_entry *)
                                kmem_cache_alloc(dlm_mle_cache, GFP_NOFS);
                        if (!mle) {
                                response = DLM_MASTER_RESP_ERROR;
                                mlog_errno(-ENOMEM);
                                goto send_response;
                        }
                        goto way_up_top;
                }

                // mlog(0, "this is second time thru, already allocated, "
                // "add the block.\n");
                dlm_init_mle(mle, DLM_MLE_BLOCK, dlm, NULL, name, namelen);
                set_bit(request->node_idx, mle->maybe_map);
                list_add(&mle->list, &dlm->master_list);
                response = DLM_MASTER_RESP_NO;
        } else {
                // mlog(0, "mle was found\n");
                set_maybe = 1;
                spin_lock(&tmpmle->spinlock);
                if (tmpmle->master == dlm->node_num) {
                        mlog(ML_ERROR, "no lockres, but an mle with this node as master!\n");
                        BUG();
                }
                if (tmpmle->type == DLM_MLE_BLOCK)
                        response = DLM_MASTER_RESP_NO;
                else if (tmpmle->type == DLM_MLE_MIGRATION) {
                        mlog(0, "migration mle was found (%u->%u)\n",
                             tmpmle->master, tmpmle->new_master);
                        /* real master can respond on its own */
                        response = DLM_MASTER_RESP_NO;
                } else
                        response = DLM_MASTER_RESP_MAYBE;
                if (set_maybe)
                        set_bit(request->node_idx, tmpmle->maybe_map);
                spin_unlock(&tmpmle->spinlock);
        }
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        if (found) {
                /* keep the mle attached to heartbeat events */
                dlm_put_mle(tmpmle);
        }
send_response:
        /*
         * __dlm_lookup_lockres() grabbed a reference to this lockres.
         * The reference is released by dlm_assert_master_worker() under
         * the call to dlm_dispatch_assert_master().  If
         * dlm_assert_master_worker() isn't called, we drop it here.
         */
        if (dispatch_assert) {
                if (response != DLM_MASTER_RESP_YES)
                        mlog(ML_ERROR, "invalid response %d\n", response);
                if (!res) {
                        mlog(ML_ERROR, "bad lockres while trying to assert!\n");
                        BUG();
                }
                mlog(0, "%u is the owner of %.*s, cleaning everyone else\n",
                             dlm->node_num, res->lockname.len, res->lockname.name);
                ret = dlm_dispatch_assert_master(dlm, res, 0, request->node_idx, 
                                                 DLM_ASSERT_MASTER_MLE_CLEANUP);
                if (ret < 0) {
                        mlog(ML_ERROR, "failed to dispatch assert master work\n");
                        response = DLM_MASTER_RESP_ERROR;
                        dlm_lockres_put(res);
                }
        } else {
                if (res)
                        dlm_lockres_put(res);
        }

        dlm_put(dlm);
        return response;
}

/*
 * DLM_ASSERT_MASTER_MSG
 */


/*
 * NOTE: this can be used for debugging
 * can periodically run all locks owned by this node
 * and re-assert across the cluster...
 */
static int dlm_do_assert_master(struct dlm_ctxt *dlm,
                                struct dlm_lock_resource *res,
                                void *nodemap, u32 flags)
{
        struct dlm_assert_master assert;
        int to, tmpret;
        struct dlm_node_iter iter;
        int ret = 0;
        int reassert;
        const char *lockname = res->lockname.name;
        unsigned int namelen = res->lockname.len;

        BUG_ON(namelen > O2NM_MAX_NAME_LEN);

        spin_lock(&res->spinlock);
        res->state |= DLM_LOCK_RES_SETREF_INPROG;
        spin_unlock(&res->spinlock);

again:
        reassert = 0;

        /* note that if this nodemap is empty, it returns 0 */
        dlm_node_iter_init(nodemap, &iter);
        while ((to = dlm_node_iter_next(&iter)) >= 0) {
                int r = 0;
                struct dlm_master_list_entry *mle = NULL;

                mlog(0, "sending assert master to %d (%.*s)\n", to,
                     namelen, lockname);
                memset(&assert, 0, sizeof(assert));
                assert.node_idx = dlm->node_num;
                assert.namelen = namelen;
                memcpy(assert.name, lockname, namelen);
                assert.flags = cpu_to_be32(flags);

                tmpret = o2net_send_message(DLM_ASSERT_MASTER_MSG, dlm->key,
                                            &assert, sizeof(assert), to, &r);
                if (tmpret < 0) {
                        mlog(0, "assert_master returned %d!\n", tmpret);
                        if (!dlm_is_host_down(tmpret)) {
                                mlog(ML_ERROR, "unhandled error=%d!\n", tmpret);
                                BUG();
                        }
                        /* a node died.  finish out the rest of the nodes. */
                        mlog(0, "link to %d went down!\n", to);
                        /* any nonzero status return will do */
                        ret = tmpret;
                        r = 0;
                } else if (r < 0) {
                        /* ok, something horribly messed.  kill thyself. */
                        mlog(ML_ERROR,"during assert master of %.*s to %u, "
                             "got %d.\n", namelen, lockname, to, r);
                        spin_lock(&dlm->spinlock);
                        spin_lock(&dlm->master_lock);
                        if (dlm_find_mle(dlm, &mle, (char *)lockname,
                                         namelen)) {
                                dlm_print_one_mle(mle);
                                __dlm_put_mle(mle);
                        }
                        spin_unlock(&dlm->master_lock);
                        spin_unlock(&dlm->spinlock);
                        BUG();
                }

                if (r & DLM_ASSERT_RESPONSE_REASSERT &&
                    !(r & DLM_ASSERT_RESPONSE_MASTERY_REF)) {
                                mlog(ML_ERROR, "%.*s: very strange, "
                                     "master MLE but no lockres on %u\n",
                                     namelen, lockname, to);
                }

                if (r & DLM_ASSERT_RESPONSE_REASSERT) {
                        mlog(0, "%.*s: node %u create mles on other "
                             "nodes and requests a re-assert\n", 
                             namelen, lockname, to);
                        reassert = 1;
                }
                if (r & DLM_ASSERT_RESPONSE_MASTERY_REF) {
                        mlog(0, "%.*s: node %u has a reference to this "
                             "lockres, set the bit in the refmap\n",
                             namelen, lockname, to);
                        spin_lock(&res->spinlock);
                        dlm_lockres_set_refmap_bit(to, res);
                        spin_unlock(&res->spinlock);
                }
        }

        if (reassert)
                goto again;

        spin_lock(&res->spinlock);
        res->state &= ~DLM_LOCK_RES_SETREF_INPROG;
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);

        return ret;
}

/*
 * locks that can be taken here:
 * dlm->spinlock
 * res->spinlock
 * mle->spinlock
 * dlm->master_list
 *
 * if possible, TRIM THIS DOWN!!!
 */
int dlm_assert_master_handler(struct o2net_msg *msg, u32 len, void *data,
                              void **ret_data)
{
        struct dlm_ctxt *dlm = data;
        struct dlm_master_list_entry *mle = NULL;
        struct dlm_assert_master *assert = (struct dlm_assert_master *)msg->buf;
        struct dlm_lock_resource *res = NULL;
        char *name;
        unsigned int namelen, hash;
        u32 flags;
        int master_request = 0, have_lockres_ref = 0;
        int ret = 0;

        if (!dlm_grab(dlm))
                return 0;

        name = assert->name;
        namelen = assert->namelen;
        hash = dlm_lockid_hash(name, namelen);
        flags = be32_to_cpu(assert->flags);

        if (namelen > DLM_LOCKID_NAME_MAX) {
                mlog(ML_ERROR, "Invalid name length!");
                goto done;
        }

        spin_lock(&dlm->spinlock);

        if (flags)
                mlog(0, "assert_master with flags: %u\n", flags);

        /* find the MLE */
        spin_lock(&dlm->master_lock);
        if (!dlm_find_mle(dlm, &mle, name, namelen)) {
                /* not an error, could be master just re-asserting */
                mlog(0, "just got an assert_master from %u, but no "
                     "MLE for it! (%.*s)\n", assert->node_idx,
                     namelen, name);
        } else {
                int bit = find_next_bit (mle->maybe_map, O2NM_MAX_NODES, 0);
                if (bit >= O2NM_MAX_NODES) {
                        /* not necessarily an error, though less likely.
                         * could be master just re-asserting. */
                        mlog(0, "no bits set in the maybe_map, but %u "
                             "is asserting! (%.*s)\n", assert->node_idx,
                             namelen, name);
                } else if (bit != assert->node_idx) {
                        if (flags & DLM_ASSERT_MASTER_MLE_CLEANUP) {
                                mlog(0, "master %u was found, %u should "
                                     "back off\n", assert->node_idx, bit);
                        } else {
                                /* with the fix for bug 569, a higher node
                                 * number winning the mastery will respond
                                 * YES to mastery requests, but this node
                                 * had no way of knowing.  let it pass. */
                                mlog(0, "%u is the lowest node, "
                                     "%u is asserting. (%.*s)  %u must "
                                     "have begun after %u won.\n", bit,
                                     assert->node_idx, namelen, name, bit,
                                     assert->node_idx);
                        }
                }
                if (mle->type == DLM_MLE_MIGRATION) {
                        if (flags & DLM_ASSERT_MASTER_MLE_CLEANUP) {
                                mlog(0, "%s:%.*s: got cleanup assert"
                                     " from %u for migration\n",
                                     dlm->name, namelen, name,
                                     assert->node_idx);
                        } else if (!(flags & DLM_ASSERT_MASTER_FINISH_MIGRATION)) {
                                mlog(0, "%s:%.*s: got unrelated assert"
                                     " from %u for migration, ignoring\n",
                                     dlm->name, namelen, name,
                                     assert->node_idx);
                                __dlm_put_mle(mle);
                                spin_unlock(&dlm->master_lock);
                                spin_unlock(&dlm->spinlock);
                                goto done;
                        }       
                }
        }
        spin_unlock(&dlm->master_lock);

        /* ok everything checks out with the MLE
         * now check to see if there is a lockres */
        res = __dlm_lookup_lockres(dlm, name, namelen, hash);
        if (res) {
                spin_lock(&res->spinlock);
                if (res->state & DLM_LOCK_RES_RECOVERING)  {
                        mlog(ML_ERROR, "%u asserting but %.*s is "
                             "RECOVERING!\n", assert->node_idx, namelen, name);
                        goto kill;
                }
                if (!mle) {
                        if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN &&
                            res->owner != assert->node_idx) {
                                mlog(ML_ERROR, "assert_master from "
                                          "%u, but current owner is "
                                          "%u! (%.*s)\n",
                                       assert->node_idx, res->owner,
                                       namelen, name);
                                goto kill;
                        }
                } else if (mle->type != DLM_MLE_MIGRATION) {
                        if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
                                /* owner is just re-asserting */
                                if (res->owner == assert->node_idx) {
                                        mlog(0, "owner %u re-asserting on "
                                             "lock %.*s\n", assert->node_idx,
                                             namelen, name);
                                        goto ok;
                                }
                                mlog(ML_ERROR, "got assert_master from "
                                     "node %u, but %u is the owner! "
                                     "(%.*s)\n", assert->node_idx,
                                     res->owner, namelen, name);
                                goto kill;
                        }
                        if (!(res->state & DLM_LOCK_RES_IN_PROGRESS)) {
                                mlog(ML_ERROR, "got assert from %u, but lock "
                                     "with no owner should be "
                                     "in-progress! (%.*s)\n",
                                     assert->node_idx,
                                     namelen, name);
                                goto kill;
                        }
                } else /* mle->type == DLM_MLE_MIGRATION */ {
                        /* should only be getting an assert from new master */
                        if (assert->node_idx != mle->new_master) {
                                mlog(ML_ERROR, "got assert from %u, but "
                                     "new master is %u, and old master "
                                     "was %u (%.*s)\n",
                                     assert->node_idx, mle->new_master,
                                     mle->master, namelen, name);
                                goto kill;
                        }

                }
ok:
                spin_unlock(&res->spinlock);
        }
        spin_unlock(&dlm->spinlock);

        // mlog(0, "woo!  got an assert_master from node %u!\n",
        //           assert->node_idx);
        if (mle) {
                int extra_ref = 0;
                int nn = -1;
                int rr, err = 0;
                
                spin_lock(&mle->spinlock);
                if (mle->type == DLM_MLE_BLOCK || mle->type == DLM_MLE_MIGRATION)
                        extra_ref = 1;
                else {
                        /* MASTER mle: if any bits set in the response map
                         * then the calling node needs to re-assert to clear
                         * up nodes that this node contacted */
                        while ((nn = find_next_bit (mle->response_map, O2NM_MAX_NODES, 
                                                    nn+1)) < O2NM_MAX_NODES) {
                                if (nn != dlm->node_num && nn != assert->node_idx)
                                        master_request = 1;
                        }
                }
                mle->master = assert->node_idx;
                atomic_set(&mle->woken, 1);
                wake_up(&mle->wq);
                spin_unlock(&mle->spinlock);

                if (res) {
                        int wake = 0;
                        spin_lock(&res->spinlock);
                        if (mle->type == DLM_MLE_MIGRATION) {
                                mlog(0, "finishing off migration of lockres %.*s, "
                                        "from %u to %u\n",
                                        res->lockname.len, res->lockname.name,
                                        dlm->node_num, mle->new_master);
                                res->state &= ~DLM_LOCK_RES_MIGRATING;
                                wake = 1;
                                dlm_change_lockres_owner(dlm, res, mle->new_master);
                                BUG_ON(res->state & DLM_LOCK_RES_DIRTY);
                        } else {
                                dlm_change_lockres_owner(dlm, res, mle->master);
                        }
                        spin_unlock(&res->spinlock);
                        have_lockres_ref = 1;
                        if (wake)
                                wake_up(&res->wq);
                }

                /* master is known, detach if not already detached.
                 * ensures that only one assert_master call will happen
                 * on this mle. */
                spin_lock(&dlm->spinlock);
                spin_lock(&dlm->master_lock);

                rr = atomic_read(&mle->mle_refs.refcount);
                if (mle->inuse > 0) {
                        if (extra_ref && rr < 3)
                                err = 1;
                        else if (!extra_ref && rr < 2)
                                err = 1;
                } else {
                        if (extra_ref && rr < 2)
                                err = 1;
                        else if (!extra_ref && rr < 1)
                                err = 1;
                }
                if (err) {
                        mlog(ML_ERROR, "%s:%.*s: got assert master from %u "
                             "that will mess up this node, refs=%d, extra=%d, "
                             "inuse=%d\n", dlm->name, namelen, name,
                             assert->node_idx, rr, extra_ref, mle->inuse);
                        dlm_print_one_mle(mle);
                }
                list_del_init(&mle->list);
                __dlm_mle_detach_hb_events(dlm, mle);
                __dlm_put_mle(mle);
                if (extra_ref) {
                        /* the assert master message now balances the extra
                         * ref given by the master / migration request message.
                         * if this is the last put, it will be removed
                         * from the list. */
                        __dlm_put_mle(mle);
                }
                spin_unlock(&dlm->master_lock);
                spin_unlock(&dlm->spinlock);
        } else if (res) {
                if (res->owner != assert->node_idx) {
                        mlog(0, "assert_master from %u, but current "
                             "owner is %u (%.*s), no mle\n", assert->node_idx,
                             res->owner, namelen, name);
                }
        }

done:
        ret = 0;
        if (res) {
                spin_lock(&res->spinlock);
                res->state |= DLM_LOCK_RES_SETREF_INPROG;
                spin_unlock(&res->spinlock);
                *ret_data = (void *)res;
        }
        dlm_put(dlm);
        if (master_request) {
                mlog(0, "need to tell master to reassert\n");
                /* positive. negative would shoot down the node. */
                ret |= DLM_ASSERT_RESPONSE_REASSERT;
                if (!have_lockres_ref) {
                        mlog(ML_ERROR, "strange, got assert from %u, MASTER "
                             "mle present here for %s:%.*s, but no lockres!\n",
                             assert->node_idx, dlm->name, namelen, name);
                }
        }
        if (have_lockres_ref) {
                /* let the master know we have a reference to the lockres */
                ret |= DLM_ASSERT_RESPONSE_MASTERY_REF;
                mlog(0, "%s:%.*s: got assert from %u, need a ref\n",
                     dlm->name, namelen, name, assert->node_idx);
        }
        return ret;

kill:
        /* kill the caller! */
        mlog(ML_ERROR, "Bad message received from another node.  Dumping state "
             "and killing the other node now!  This node is OK and can continue.\n");
        __dlm_print_one_lock_resource(res);
        spin_unlock(&res->spinlock);
        spin_unlock(&dlm->spinlock);
        *ret_data = (void *)res; 
        dlm_put(dlm);
        return -EINVAL;
}

void dlm_assert_master_post_handler(int status, void *data, void *ret_data)
{
        struct dlm_lock_resource *res = (struct dlm_lock_resource *)ret_data;

        if (ret_data) {
                spin_lock(&res->spinlock);
                res->state &= ~DLM_LOCK_RES_SETREF_INPROG;
                spin_unlock(&res->spinlock);
                wake_up(&res->wq);
                dlm_lockres_put(res);
        }
        return;
}

int dlm_dispatch_assert_master(struct dlm_ctxt *dlm,
                               struct dlm_lock_resource *res,
                               int ignore_higher, u8 request_from, u32 flags)
{
        struct dlm_work_item *item;
        item = kzalloc(sizeof(*item), GFP_NOFS);
        if (!item)
                return -ENOMEM;


        /* queue up work for dlm_assert_master_worker */
        dlm_grab(dlm);  /* get an extra ref for the work item */
        dlm_init_work_item(dlm, item, dlm_assert_master_worker, NULL);
        item->u.am.lockres = res; /* already have a ref */
        /* can optionally ignore node numbers higher than this node */
        item->u.am.ignore_higher = ignore_higher;
        item->u.am.request_from = request_from;
        item->u.am.flags = flags;

        if (ignore_higher) 
                mlog(0, "IGNORE HIGHER: %.*s\n", res->lockname.len, 
                     res->lockname.name);
                
        spin_lock(&dlm->work_lock);
        list_add_tail(&item->list, &dlm->work_list);
        spin_unlock(&dlm->work_lock);

        queue_work(dlm->dlm_worker, &dlm->dispatched_work);
        return 0;
}

static void dlm_assert_master_worker(struct dlm_work_item *item, void *data)
{
        struct dlm_ctxt *dlm = data;
        int ret = 0;
        struct dlm_lock_resource *res;
        unsigned long nodemap[BITS_TO_LONGS(O2NM_MAX_NODES)];
        int ignore_higher;
        int bit;
        u8 request_from;
        u32 flags;

        dlm = item->dlm;
        res = item->u.am.lockres;
        ignore_higher = item->u.am.ignore_higher;
        request_from = item->u.am.request_from;
        flags = item->u.am.flags;

        spin_lock(&dlm->spinlock);
        memcpy(nodemap, dlm->domain_map, sizeof(nodemap));
        spin_unlock(&dlm->spinlock);

        clear_bit(dlm->node_num, nodemap);
        if (ignore_higher) {
                /* if is this just to clear up mles for nodes below
                 * this node, do not send the message to the original
                 * caller or any node number higher than this */
                clear_bit(request_from, nodemap);
                bit = dlm->node_num;
                while (1) {
                        bit = find_next_bit(nodemap, O2NM_MAX_NODES,
                                            bit+1);
                        if (bit >= O2NM_MAX_NODES)
                                break;
                        clear_bit(bit, nodemap);
                }
        }

        /*
         * If we're migrating this lock to someone else, we are no
         * longer allowed to assert out own mastery.  OTOH, we need to
         * prevent migration from starting while we're still asserting
         * our dominance.  The reserved ast delays migration.
         */
        spin_lock(&res->spinlock);
        if (res->state & DLM_LOCK_RES_MIGRATING) {
                mlog(0, "Someone asked us to assert mastery, but we're "
                     "in the middle of migration.  Skipping assert, "
                     "the new master will handle that.\n");
                spin_unlock(&res->spinlock);
                goto put;
        } else
                __dlm_lockres_reserve_ast(res);
        spin_unlock(&res->spinlock);

        /* this call now finishes out the nodemap
         * even if one or more nodes die */
        mlog(0, "worker about to master %.*s here, this=%u\n",
                     res->lockname.len, res->lockname.name, dlm->node_num);
        ret = dlm_do_assert_master(dlm, res, nodemap, flags);
        if (ret < 0) {
                /* no need to restart, we are done */
                if (!dlm_is_host_down(ret))
                        mlog_errno(ret);
        }

        /* Ok, we've asserted ourselves.  Let's let migration start. */
        dlm_lockres_release_ast(dlm, res);

put:
        dlm_lockres_put(res);

        mlog(0, "finished with dlm_assert_master_worker\n");
}

/* SPECIAL CASE for the $RECOVERY lock used by the recovery thread.
 * We cannot wait for node recovery to complete to begin mastering this
 * lockres because this lockres is used to kick off recovery! ;-)
 * So, do a pre-check on all living nodes to see if any of those nodes
 * think that $RECOVERY is currently mastered by a dead node.  If so,
 * we wait a short time to allow that node to get notified by its own
 * heartbeat stack, then check again.  All $RECOVERY lock resources
 * mastered by dead nodes are purged when the hearbeat callback is 
 * fired, so we can know for sure that it is safe to continue once
 * the node returns a live node or no node.  */
static int dlm_pre_master_reco_lockres(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res)
{
        struct dlm_node_iter iter;
        int nodenum;
        int ret = 0;
        u8 master = DLM_LOCK_RES_OWNER_UNKNOWN;

        spin_lock(&dlm->spinlock);
        dlm_node_iter_init(dlm->domain_map, &iter);
        spin_unlock(&dlm->spinlock);

        while ((nodenum = dlm_node_iter_next(&iter)) >= 0) {
                /* do not send to self */
                if (nodenum == dlm->node_num)
                        continue;
                ret = dlm_do_master_requery(dlm, res, nodenum, &master);
                if (ret < 0) {
                        mlog_errno(ret);
                        if (!dlm_is_host_down(ret))
                                BUG();
                        /* host is down, so answer for that node would be
                         * DLM_LOCK_RES_OWNER_UNKNOWN.  continue. */
                        ret = 0;
                }

                if (master != DLM_LOCK_RES_OWNER_UNKNOWN) {
                        /* check to see if this master is in the recovery map */
                        spin_lock(&dlm->spinlock);
                        if (test_bit(master, dlm->recovery_map)) {
                                mlog(ML_NOTICE, "%s: node %u has not seen "
                                     "node %u go down yet, and thinks the "
                                     "dead node is mastering the recovery "
                                     "lock.  must wait.\n", dlm->name,
                                     nodenum, master);
                                ret = -EAGAIN;
                        }
                        spin_unlock(&dlm->spinlock);
                        mlog(0, "%s: reco lock master is %u\n", dlm->name, 
                             master);
                        break;
                }
        }
        return ret;
}

/*
 * DLM_DEREF_LOCKRES_MSG
 */

int dlm_drop_lockres_ref(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
{
        struct dlm_deref_lockres deref;
        int ret = 0, r;
        const char *lockname;
        unsigned int namelen;

        lockname = res->lockname.name;
        namelen = res->lockname.len;
        BUG_ON(namelen > O2NM_MAX_NAME_LEN);

        mlog(0, "%s:%.*s: sending deref to %d\n",
             dlm->name, namelen, lockname, res->owner);
        memset(&deref, 0, sizeof(deref));
        deref.node_idx = dlm->node_num;
        deref.namelen = namelen;
        memcpy(deref.name, lockname, namelen);

        ret = o2net_send_message(DLM_DEREF_LOCKRES_MSG, dlm->key,
                                 &deref, sizeof(deref), res->owner, &r);
        if (ret < 0)
                mlog_errno(ret);
        else if (r < 0) {
                /* BAD.  other node says I did not have a ref. */
                mlog(ML_ERROR,"while dropping ref on %s:%.*s "
                    "(master=%u) got %d.\n", dlm->name, namelen,
                    lockname, res->owner, r);
                dlm_print_one_lock_resource(res);
                BUG();
        }
        return ret;
}

int dlm_deref_lockres_handler(struct o2net_msg *msg, u32 len, void *data,
                              void **ret_data)
{
        struct dlm_ctxt *dlm = data;
        struct dlm_deref_lockres *deref = (struct dlm_deref_lockres *)msg->buf;
        struct dlm_lock_resource *res = NULL;
        char *name;
        unsigned int namelen;
        int ret = -EINVAL;
        u8 node;
        unsigned int hash;
        struct dlm_work_item *item;
        int cleared = 0;
        int dispatch = 0;

        if (!dlm_grab(dlm))
                return 0;

        name = deref->name;
        namelen = deref->namelen;
        node = deref->node_idx;

        if (namelen > DLM_LOCKID_NAME_MAX) {
                mlog(ML_ERROR, "Invalid name length!");
                goto done;
        }
        if (deref->node_idx >= O2NM_MAX_NODES) {
                mlog(ML_ERROR, "Invalid node number: %u\n", node);
                goto done;
        }

        hash = dlm_lockid_hash(name, namelen);

        spin_lock(&dlm->spinlock);
        res = __dlm_lookup_lockres_full(dlm, name, namelen, hash);
        if (!res) {
                spin_unlock(&dlm->spinlock);
                mlog(ML_ERROR, "%s:%.*s: bad lockres name\n",
                     dlm->name, namelen, name);
                goto done;
        }
        spin_unlock(&dlm->spinlock);

        spin_lock(&res->spinlock);
        if (res->state & DLM_LOCK_RES_SETREF_INPROG)
                dispatch = 1;
        else {
                BUG_ON(res->state & DLM_LOCK_RES_DROPPING_REF);
                if (test_bit(node, res->refmap)) {
                        dlm_lockres_clear_refmap_bit(node, res);
                        cleared = 1;
                }
        }
        spin_unlock(&res->spinlock);

        if (!dispatch) {
                if (cleared)
                        dlm_lockres_calc_usage(dlm, res);
                else {
                        mlog(ML_ERROR, "%s:%.*s: node %u trying to drop ref "
                        "but it is already dropped!\n", dlm->name,
                        res->lockname.len, res->lockname.name, node);
                        dlm_print_one_lock_resource(res);
                }
                ret = 0;
                goto done;
        }

        item = kzalloc(sizeof(*item), GFP_NOFS);
        if (!item) {
                ret = -ENOMEM;
                mlog_errno(ret);
                goto done;
        }

        dlm_init_work_item(dlm, item, dlm_deref_lockres_worker, NULL);
        item->u.dl.deref_res = res;
        item->u.dl.deref_node = node;

        spin_lock(&dlm->work_lock);
        list_add_tail(&item->list, &dlm->work_list);
        spin_unlock(&dlm->work_lock);

        queue_work(dlm->dlm_worker, &dlm->dispatched_work);
        return 0;

done:
        if (res)
                dlm_lockres_put(res);
        dlm_put(dlm);

        return ret;
}

static void dlm_deref_lockres_worker(struct dlm_work_item *item, void *data)
{
        struct dlm_ctxt *dlm;
        struct dlm_lock_resource *res;
        u8 node;
        u8 cleared = 0;

        dlm = item->dlm;
        res = item->u.dl.deref_res;
        node = item->u.dl.deref_node;

        spin_lock(&res->spinlock);
        BUG_ON(res->state & DLM_LOCK_RES_DROPPING_REF);
        if (test_bit(node, res->refmap)) {
                __dlm_wait_on_lockres_flags(res, DLM_LOCK_RES_SETREF_INPROG);
                dlm_lockres_clear_refmap_bit(node, res);
                cleared = 1;
        }
        spin_unlock(&res->spinlock);

        if (cleared) {
                mlog(0, "%s:%.*s node %u ref dropped in dispatch\n",
                     dlm->name, res->lockname.len, res->lockname.name, node);
                dlm_lockres_calc_usage(dlm, res);
        } else {
                mlog(ML_ERROR, "%s:%.*s: node %u trying to drop ref "
                     "but it is already dropped!\n", dlm->name,
                     res->lockname.len, res->lockname.name, node);
                dlm_print_one_lock_resource(res);
        }

        dlm_lockres_put(res);
}

/* Checks whether the lockres can be migrated. Returns 0 if yes, < 0
 * if not. If 0, numlocks is set to the number of locks in the lockres.
 */
static int dlm_is_lockres_migrateable(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res,
                                      int *numlocks)
{
        int ret;
        int i;
        int count = 0;
        struct list_head *queue;
        struct dlm_lock *lock;

        assert_spin_locked(&res->spinlock);

        ret = -EINVAL;
        if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
                mlog(0, "cannot migrate lockres with unknown owner!\n");
                goto leave;
        }

        if (res->owner != dlm->node_num) {
                mlog(0, "cannot migrate lockres this node doesn't own!\n");
                goto leave;
        }

        ret = 0;
        queue = &res->granted;
        for (i = 0; i < 3; i++) {
                list_for_each_entry(lock, queue, list) {
                        ++count;
                        if (lock->ml.node == dlm->node_num) {
                                mlog(0, "found a lock owned by this node still "
                                     "on the %s queue!  will not migrate this "
                                     "lockres\n", (i == 0 ? "granted" :
                                                   (i == 1 ? "converting" :
                                                    "blocked")));
                                ret = -ENOTEMPTY;
                                goto leave;
                        }
                }
                queue++;
        }

        *numlocks = count;
        mlog(0, "migrateable lockres having %d locks\n", *numlocks);

leave:
        return ret;
}

/*
 * DLM_MIGRATE_LOCKRES
 */


static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
                               struct dlm_lock_resource *res,
                               u8 target)
{
        struct dlm_master_list_entry *mle = NULL;
        struct dlm_master_list_entry *oldmle = NULL;
        struct dlm_migratable_lockres *mres = NULL;
        int ret = 0;
        const char *name;
        unsigned int namelen;
        int mle_added = 0;
        int numlocks;
        int wake = 0;

        if (!dlm_grab(dlm))
                return -EINVAL;

        name = res->lockname.name;
        namelen = res->lockname.len;

        mlog(0, "migrating %.*s to %u\n", namelen, name, target);

        /*
         * ensure this lockres is a proper candidate for migration
         */
        spin_lock(&res->spinlock);
        ret = dlm_is_lockres_migrateable(dlm, res, &numlocks);
        if (ret < 0) {
                spin_unlock(&res->spinlock);
                goto leave;
        }
        spin_unlock(&res->spinlock);

        /* no work to do */
        if (numlocks == 0) {
                mlog(0, "no locks were found on this lockres! done!\n");
                goto leave;
        }

        /*
         * preallocate up front
         * if this fails, abort
         */

        ret = -ENOMEM;
        mres = (struct dlm_migratable_lockres *) __get_free_page(GFP_NOFS);
        if (!mres) {
                mlog_errno(ret);
                goto leave;
        }

        mle = (struct dlm_master_list_entry *) kmem_cache_alloc(dlm_mle_cache,
                                                                GFP_NOFS);
        if (!mle) {
                mlog_errno(ret);
                goto leave;
        }
        ret = 0;

        /*
         * find a node to migrate the lockres to
         */

        mlog(0, "picking a migration node\n");
        spin_lock(&dlm->spinlock);
        /* pick a new node */
        if (!test_bit(target, dlm->domain_map) ||
            target >= O2NM_MAX_NODES) {
                target = dlm_pick_migration_target(dlm, res);
        }
        mlog(0, "node %u chosen for migration\n", target);

        if (target >= O2NM_MAX_NODES ||
            !test_bit(target, dlm->domain_map)) {
                /* target chosen is not alive */
                ret = -EINVAL;
        }

        if (ret) {
                spin_unlock(&dlm->spinlock);
                goto fail;
        }

        mlog(0, "continuing with target = %u\n", target);

        /*
         * clear any existing master requests and
         * add the migration mle to the list
         */
        spin_lock(&dlm->master_lock);
        ret = dlm_add_migration_mle(dlm, res, mle, &oldmle, name,
                                    namelen, target, dlm->node_num);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        if (ret == -EEXIST) {
                mlog(0, "another process is already migrating it\n");
                goto fail;
        }
        mle_added = 1;

        /*
         * set the MIGRATING flag and flush asts
         * if we fail after this we need to re-dirty the lockres
         */
        if (dlm_mark_lockres_migrating(dlm, res, target) < 0) {
                mlog(ML_ERROR, "tried to migrate %.*s to %u, but "
                     "the target went down.\n", res->lockname.len,
                     res->lockname.name, target);
                spin_lock(&res->spinlock);
                res->state &= ~DLM_LOCK_RES_MIGRATING;
                wake = 1;
                spin_unlock(&res->spinlock);
                ret = -EINVAL;
        }

fail:
        if (oldmle) {
                /* master is known, detach if not already detached */
                dlm_mle_detach_hb_events(dlm, oldmle);
                dlm_put_mle(oldmle);
        }

        if (ret < 0) {
                if (mle_added) {
                        dlm_mle_detach_hb_events(dlm, mle);
                        dlm_put_mle(mle);
                } else if (mle) {
                        kmem_cache_free(dlm_mle_cache, mle);
                }
                goto leave;
        }

        /*
         * at this point, we have a migration target, an mle
         * in the master list, and the MIGRATING flag set on
         * the lockres
         */

        /* now that remote nodes are spinning on the MIGRATING flag,
         * ensure that all assert_master work is flushed. */
        flush_workqueue(dlm->dlm_worker);

        /* get an extra reference on the mle.
         * otherwise the assert_master from the new
         * master will destroy this.
         * also, make sure that all callers of dlm_get_mle
         * take both dlm->spinlock and dlm->master_lock */
        spin_lock(&dlm->spinlock);
        spin_lock(&dlm->master_lock);
        dlm_get_mle_inuse(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        /* notify new node and send all lock state */
        /* call send_one_lockres with migration flag.
         * this serves as notice to the target node that a
         * migration is starting. */
        ret = dlm_send_one_lockres(dlm, res, mres, target,
                                   DLM_MRES_MIGRATION);

        if (ret < 0) {
                mlog(0, "migration to node %u failed with %d\n",
                     target, ret);
                /* migration failed, detach and clean up mle */
                dlm_mle_detach_hb_events(dlm, mle);
                dlm_put_mle(mle);
                dlm_put_mle_inuse(mle);
                spin_lock(&res->spinlock);
                res->state &= ~DLM_LOCK_RES_MIGRATING;
                wake = 1;
                spin_unlock(&res->spinlock);
                goto leave;
        }

        /* at this point, the target sends a message to all nodes,
         * (using dlm_do_migrate_request).  this node is skipped since
         * we had to put an mle in the list to begin the process.  this
         * node now waits for target to do an assert master.  this node
         * will be the last one notified, ensuring that the migration
         * is complete everywhere.  if the target dies while this is
         * going on, some nodes could potentially see the target as the
         * master, so it is important that my recovery finds the migration
         * mle and sets the master to UNKNONWN. */


        /* wait for new node to assert master */
        while (1) {
                ret = wait_event_interruptible_timeout(mle->wq,
                                        (atomic_read(&mle->woken) == 1),
                                        msecs_to_jiffies(5000));

                if (ret >= 0) {
                        if (atomic_read(&mle->woken) == 1 ||
                            res->owner == target)
                                break;

                        mlog(0, "%s:%.*s: timed out during migration\n",
                             dlm->name, res->lockname.len, res->lockname.name);
                        /* avoid hang during shutdown when migrating lockres 
                         * to a node which also goes down */
                        if (dlm_is_node_dead(dlm, target)) {
                                mlog(0, "%s:%.*s: expected migration "
                                     "target %u is no longer up, restarting\n",
                                     dlm->name, res->lockname.len,
                                     res->lockname.name, target);
                                ret = -EINVAL;
                                /* migration failed, detach and clean up mle */
                                dlm_mle_detach_hb_events(dlm, mle);
                                dlm_put_mle(mle);
                                dlm_put_mle_inuse(mle);
                                spin_lock(&res->spinlock);
                                res->state &= ~DLM_LOCK_RES_MIGRATING;
                                wake = 1;
                                spin_unlock(&res->spinlock);
                                goto leave;
                        }
                } else
                        mlog(0, "%s:%.*s: caught signal during migration\n",
                             dlm->name, res->lockname.len, res->lockname.name);
        }

        /* all done, set the owner, clear the flag */
        spin_lock(&res->spinlock);
        dlm_set_lockres_owner(dlm, res, target);
        res->state &= ~DLM_LOCK_RES_MIGRATING;
        dlm_remove_nonlocal_locks(dlm, res);
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);

        /* master is known, detach if not already detached */
        dlm_mle_detach_hb_events(dlm, mle);
        dlm_put_mle_inuse(mle);
        ret = 0;

        dlm_lockres_calc_usage(dlm, res);

leave:
        /* re-dirty the lockres if we failed */
        if (ret < 0)
                dlm_kick_thread(dlm, res);

        /* wake up waiters if the MIGRATING flag got set
         * but migration failed */
        if (wake)
                wake_up(&res->wq);

        /* TODO: cleanup */
        if (mres)
                free_page((unsigned long)mres);

        dlm_put(dlm);

        mlog(0, "returning %d\n", ret);
        return ret;
}

#define DLM_MIGRATION_RETRY_MS  100

/* Should be called only after beginning the domain leave process.
 * There should not be any remaining locks on nonlocal lock resources,
 * and there should be no local locks left on locally mastered resources.
 *
 * Called with the dlm spinlock held, may drop it to do migration, but
 * will re-acquire before exit.
 *
 * Returns: 1 if dlm->spinlock was dropped/retaken, 0 if never dropped */
int dlm_empty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
{
        int ret;
        int lock_dropped = 0;
        int numlocks;

        spin_lock(&res->spinlock);
        if (res->owner != dlm->node_num) {
                if (!__dlm_lockres_unused(res)) {
                        mlog(ML_ERROR, "%s:%.*s: this node is not master, "
                             "trying to free this but locks remain\n",
                             dlm->name, res->lockname.len, res->lockname.name);
                }
                spin_unlock(&res->spinlock);
                goto leave;
        }

        /* No need to migrate a lockres having no locks */
        ret = dlm_is_lockres_migrateable(dlm, res, &numlocks);
        if (ret >= 0 && numlocks == 0) {
                spin_unlock(&res->spinlock);
                goto leave;
        }
        spin_unlock(&res->spinlock);

        /* Wheee! Migrate lockres here! Will sleep so drop spinlock. */
        spin_unlock(&dlm->spinlock);
        lock_dropped = 1;
        while (1) {
                ret = dlm_migrate_lockres(dlm, res, O2NM_MAX_NODES);
                if (ret >= 0)
                        break;
                if (ret == -ENOTEMPTY) {
                        mlog(ML_ERROR, "lockres %.*s still has local locks!\n",
                                res->lockname.len, res->lockname.name);
                        BUG();
                }

                mlog(0, "lockres %.*s: migrate failed, "
                     "retrying\n", res->lockname.len,
                     res->lockname.name);
                msleep(DLM_MIGRATION_RETRY_MS);
        }
        spin_lock(&dlm->spinlock);
leave:
        return lock_dropped;
}

int dlm_lock_basts_flushed(struct dlm_ctxt *dlm, struct dlm_lock *lock)
{
        int ret;
        spin_lock(&dlm->ast_lock);
        spin_lock(&lock->spinlock);
        ret = (list_empty(&lock->bast_list) && !lock->bast_pending);
        spin_unlock(&lock->spinlock);
        spin_unlock(&dlm->ast_lock);
        return ret;
}

static int dlm_migration_can_proceed(struct dlm_ctxt *dlm,
                                     struct dlm_lock_resource *res,
                                     u8 mig_target)
{
        int can_proceed;
        spin_lock(&res->spinlock);
        can_proceed = !!(res->state & DLM_LOCK_RES_MIGRATING);
        spin_unlock(&res->spinlock);

        /* target has died, so make the caller break out of the 
         * wait_event, but caller must recheck the domain_map */
        spin_lock(&dlm->spinlock);
        if (!test_bit(mig_target, dlm->domain_map))
                can_proceed = 1;
        spin_unlock(&dlm->spinlock);
        return can_proceed;
}

static int dlm_lockres_is_dirty(struct dlm_ctxt *dlm,
                                struct dlm_lock_resource *res)
{
        int ret;
        spin_lock(&res->spinlock);
        ret = !!(res->state & DLM_LOCK_RES_DIRTY);
        spin_unlock(&res->spinlock);
        return ret;
}


static int dlm_mark_lockres_migrating(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res,
                                       u8 target)
{
        int ret = 0;

        mlog(0, "dlm_mark_lockres_migrating: %.*s, from %u to %u\n",
               res->lockname.len, res->lockname.name, dlm->node_num,
               target);
        /* need to set MIGRATING flag on lockres.  this is done by
         * ensuring that all asts have been flushed for this lockres. */
        spin_lock(&res->spinlock);
        BUG_ON(res->migration_pending);
        res->migration_pending = 1;
        /* strategy is to reserve an extra ast then release
         * it below, letting the release do all of the work */
        __dlm_lockres_reserve_ast(res);
        spin_unlock(&res->spinlock);

        /* now flush all the pending asts */
        dlm_kick_thread(dlm, res);
        /* before waiting on DIRTY, block processes which may
         * try to dirty the lockres before MIGRATING is set */
        spin_lock(&res->spinlock);
        BUG_ON(res->state & DLM_LOCK_RES_BLOCK_DIRTY);
        res->state |= DLM_LOCK_RES_BLOCK_DIRTY;
        spin_unlock(&res->spinlock);
        /* now wait on any pending asts and the DIRTY state */
        wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
        dlm_lockres_release_ast(dlm, res);

        mlog(0, "about to wait on migration_wq, dirty=%s\n",
               res->state & DLM_LOCK_RES_DIRTY ? "yes" : "no");
        /* if the extra ref we just put was the final one, this
         * will pass thru immediately.  otherwise, we need to wait
         * for the last ast to finish. */
again:
        ret = wait_event_interruptible_timeout(dlm->migration_wq,
                   dlm_migration_can_proceed(dlm, res, target),
                   msecs_to_jiffies(1000));
        if (ret < 0) {
                mlog(0, "woken again: migrating? %s, dead? %s\n",
                       res->state & DLM_LOCK_RES_MIGRATING ? "yes":"no",
                       test_bit(target, dlm->domain_map) ? "no":"yes");
        } else {
                mlog(0, "all is well: migrating? %s, dead? %s\n",
                       res->state & DLM_LOCK_RES_MIGRATING ? "yes":"no",
                       test_bit(target, dlm->domain_map) ? "no":"yes");
        }
        if (!dlm_migration_can_proceed(dlm, res, target)) {
                mlog(0, "trying again...\n");
                goto again;
        }
        /* now that we are sure the MIGRATING state is there, drop
         * the unneded state which blocked threads trying to DIRTY */
        spin_lock(&res->spinlock);
        BUG_ON(!(res->state & DLM_LOCK_RES_BLOCK_DIRTY));
        BUG_ON(!(res->state & DLM_LOCK_RES_MIGRATING));
        res->state &= ~DLM_LOCK_RES_BLOCK_DIRTY;
        spin_unlock(&res->spinlock);

        /* did the target go down or die? */
        spin_lock(&dlm->spinlock);
        if (!test_bit(target, dlm->domain_map)) {
                mlog(ML_ERROR, "aha. migration target %u just went down\n",
                     target);
                ret = -EHOSTDOWN;
        }
        spin_unlock(&dlm->spinlock);

        /*
         * at this point:
         *
         *   o the DLM_LOCK_RES_MIGRATING flag is set
         *   o there are no pending asts on this lockres
         *   o all processes trying to reserve an ast on this
         *     lockres must wait for the MIGRATING flag to clear
         */
        return ret;
}

/* last step in the migration process.
 * original master calls this to free all of the dlm_lock
 * structures that used to be for other nodes. */
static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res)
{
        struct list_head *queue = &res->granted;
        int i, bit;
        struct dlm_lock *lock, *next;

        assert_spin_locked(&res->spinlock);

        BUG_ON(res->owner == dlm->node_num);

        for (i=0; i<3; i++) {
                list_for_each_entry_safe(lock, next, queue, list) {
                        if (lock->ml.node != dlm->node_num) {
                                mlog(0, "putting lock for node %u\n",
                                     lock->ml.node);
                                /* be extra careful */
                                BUG_ON(!list_empty(&lock->ast_list));
                                BUG_ON(!list_empty(&lock->bast_list));
                                BUG_ON(lock->ast_pending);
                                BUG_ON(lock->bast_pending);
                                dlm_lockres_clear_refmap_bit(lock->ml.node, res);
                                list_del_init(&lock->list);
                                dlm_lock_put(lock);
                                /* In a normal unlock, we would have added a
                                 * DLM_UNLOCK_FREE_LOCK action. Force it. */
                                dlm_lock_put(lock);
                        }
                }
                queue++;
        }
        bit = 0;
        while (1) {
                bit = find_next_bit(res->refmap, O2NM_MAX_NODES, bit);
                if (bit >= O2NM_MAX_NODES)
                        break;
                /* do not clear the local node reference, if there is a
                 * process holding this, let it drop the ref itself */
                if (bit != dlm->node_num) {
                        mlog(0, "%s:%.*s: node %u had a ref to this "
                             "migrating lockres, clearing\n", dlm->name,
                             res->lockname.len, res->lockname.name, bit);
                        dlm_lockres_clear_refmap_bit(bit, res);
                }
                bit++;
        }
}

/* for now this is not too intelligent.  we will
 * need stats to make this do the right thing.
 * this just finds the first lock on one of the
 * queues and uses that node as the target. */
static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res)
{
        int i;
        struct list_head *queue = &res->granted;
        struct dlm_lock *lock;
        int nodenum;

        assert_spin_locked(&dlm->spinlock);

        spin_lock(&res->spinlock);
        for (i=0; i<3; i++) {
                list_for_each_entry(lock, queue, list) {
                        /* up to the caller to make sure this node
                         * is alive */
                        if (lock->ml.node != dlm->node_num) {
                                spin_unlock(&res->spinlock);
                                return lock->ml.node;
                        }
                }
                queue++;
        }
        spin_unlock(&res->spinlock);
        mlog(0, "have not found a suitable target yet! checking domain map\n");

        /* ok now we're getting desperate.  pick anyone alive. */
        nodenum = -1;
        while (1) {
                nodenum = find_next_bit(dlm->domain_map,
                                        O2NM_MAX_NODES, nodenum+1);
                mlog(0, "found %d in domain map\n", nodenum);
                if (nodenum >= O2NM_MAX_NODES)
                        break;
                if (nodenum != dlm->node_num) {
                        mlog(0, "picking %d\n", nodenum);
                        return nodenum;
                }
        }

        mlog(0, "giving up.  no master to migrate to\n");
        return DLM_LOCK_RES_OWNER_UNKNOWN;
}



/* this is called by the new master once all lockres
 * data has been received */
static int dlm_do_migrate_request(struct dlm_ctxt *dlm,
                                  struct dlm_lock_resource *res,
                                  u8 master, u8 new_master,
                                  struct dlm_node_iter *iter)
{
        struct dlm_migrate_request migrate;
        int ret, skip, status = 0;
        int nodenum;

        memset(&migrate, 0, sizeof(migrate));
        migrate.namelen = res->lockname.len;
        memcpy(migrate.name, res->lockname.name, migrate.namelen);
        migrate.new_master = new_master;
        migrate.master = master;

        ret = 0;

        /* send message to all nodes, except the master and myself */
        while ((nodenum = dlm_node_iter_next(iter)) >= 0) {
                if (nodenum == master ||
                    nodenum == new_master)
                        continue;

                /* We could race exit domain. If exited, skip. */
                spin_lock(&dlm->spinlock);
                skip = (!test_bit(nodenum, dlm->domain_map));
                spin_unlock(&dlm->spinlock);
                if (skip) {
                        clear_bit(nodenum, iter->node_map);
                        continue;
                }

                ret = o2net_send_message(DLM_MIGRATE_REQUEST_MSG, dlm->key,
                                         &migrate, sizeof(migrate), nodenum,
                                         &status);
                if (ret < 0) {
                        mlog(0, "migrate_request returned %d!\n", ret);
                        if (!dlm_is_host_down(ret)) {
                                mlog(ML_ERROR, "unhandled error=%d!\n", ret);
                                BUG();
                        }
                        clear_bit(nodenum, iter->node_map);
                        ret = 0;
                } else if (status < 0) {
                        mlog(0, "migrate request (node %u) returned %d!\n",
                             nodenum, status);
                        ret = status;
                } else if (status == DLM_MIGRATE_RESPONSE_MASTERY_REF) {
                        /* during the migration request we short-circuited
                         * the mastery of the lockres.  make sure we have
                         * a mastery ref for nodenum */
                        mlog(0, "%s:%.*s: need ref for node %u\n",
                             dlm->name, res->lockname.len, res->lockname.name,
                             nodenum);
                        spin_lock(&res->spinlock);
                        dlm_lockres_set_refmap_bit(nodenum, res);
                        spin_unlock(&res->spinlock);
                }
        }

        if (ret < 0)
                mlog_errno(ret);

        mlog(0, "returning ret=%d\n", ret);
        return ret;
}


/* if there is an existing mle for this lockres, we now know who the master is.
 * (the one who sent us *this* message) we can clear it up right away.
 * since the process that put the mle on the list still has a reference to it,
 * we can unhash it now, set the master and wake the process.  as a result,
 * we will have no mle in the list to start with.  now we can add an mle for
 * the migration and this should be the only one found for those scanning the
 * list.  */
int dlm_migrate_request_handler(struct o2net_msg *msg, u32 len, void *data,
                                void **ret_data)
{
        struct dlm_ctxt *dlm = data;
        struct dlm_lock_resource *res = NULL;
        struct dlm_migrate_request *migrate = (struct dlm_migrate_request *) msg->buf;
        struct dlm_master_list_entry *mle = NULL, *oldmle = NULL;
        const char *name;
        unsigned int namelen, hash;
        int ret = 0;

        if (!dlm_grab(dlm))
                return -EINVAL;

        name = migrate->name;
        namelen = migrate->namelen;
        hash = dlm_lockid_hash(name, namelen);

        /* preallocate.. if this fails, abort */
        mle = (struct dlm_master_list_entry *) kmem_cache_alloc(dlm_mle_cache,
                                                         GFP_NOFS);

        if (!mle) {
                ret = -ENOMEM;
                goto leave;
        }

        /* check for pre-existing lock */
        spin_lock(&dlm->spinlock);
        res = __dlm_lookup_lockres(dlm, name, namelen, hash);
        spin_lock(&dlm->master_lock);

        if (res) {
                spin_lock(&res->spinlock);
                if (res->state & DLM_LOCK_RES_RECOVERING) {
                        /* if all is working ok, this can only mean that we got
                        * a migrate request from a node that we now see as
                        * dead.  what can we do here?  drop it to the floor? */
                        spin_unlock(&res->spinlock);
                        mlog(ML_ERROR, "Got a migrate request, but the "
                             "lockres is marked as recovering!");
                        kmem_cache_free(dlm_mle_cache, mle);
                        ret = -EINVAL; /* need a better solution */
                        goto unlock;
                }
                res->state |= DLM_LOCK_RES_MIGRATING;
                spin_unlock(&res->spinlock);
        }

        /* ignore status.  only nonzero status would BUG. */
        ret = dlm_add_migration_mle(dlm, res, mle, &oldmle,
                                    name, namelen,
                                    migrate->new_master,
                                    migrate->master);

unlock:
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        if (oldmle) {
                /* master is known, detach if not already detached */
                dlm_mle_detach_hb_events(dlm, oldmle);
                dlm_put_mle(oldmle);
        }

        if (res)
                dlm_lockres_put(res);
leave:
        dlm_put(dlm);
        return ret;
}

/* must be holding dlm->spinlock and dlm->master_lock
 * when adding a migration mle, we can clear any other mles
 * in the master list because we know with certainty that
 * the master is "master".  so we remove any old mle from
 * the list after setting it's master field, and then add
 * the new migration mle.  this way we can hold with the rule
 * of having only one mle for a given lock name at all times. */
static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
                                 struct dlm_lock_resource *res,
                                 struct dlm_master_list_entry *mle,
                                 struct dlm_master_list_entry **oldmle,
                                 const char *name, unsigned int namelen,
                                 u8 new_master, u8 master)
{
        int found;
        int ret = 0;

        *oldmle = NULL;

        mlog_entry_void();

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);

        /* caller is responsible for any ref taken here on oldmle */
        found = dlm_find_mle(dlm, oldmle, (char *)name, namelen);
        if (found) {
                struct dlm_master_list_entry *tmp = *oldmle;
                spin_lock(&tmp->spinlock);
                if (tmp->type == DLM_MLE_MIGRATION) {
                        if (master == dlm->node_num) {
                                /* ah another process raced me to it */
                                mlog(0, "tried to migrate %.*s, but some "
                                     "process beat me to it\n",
                                     namelen, name);
                                ret = -EEXIST;
                        } else {
                                /* bad.  2 NODES are trying to migrate! */
                                mlog(ML_ERROR, "migration error  mle: "
                                     "master=%u new_master=%u // request: "
                                     "master=%u new_master=%u // "
                                     "lockres=%.*s\n",
                                     tmp->master, tmp->new_master,
                                     master, new_master,
                                     namelen, name);
                                BUG();
                        }
                } else {
                        /* this is essentially what assert_master does */
                        tmp->master = master;
                        atomic_set(&tmp->woken, 1);
                        wake_up(&tmp->wq);
                        /* remove it from the list so that only one
                         * mle will be found */
                        list_del_init(&tmp->list);
                        /* this was obviously WRONG.  mle is uninited here.  should be tmp. */
                        __dlm_mle_detach_hb_events(dlm, tmp);
                        ret = DLM_MIGRATE_RESPONSE_MASTERY_REF;
                        mlog(0, "%s:%.*s: master=%u, newmaster=%u, "
                            "telling master to get ref for cleared out mle "
                            "during migration\n", dlm->name, namelen, name,
                            master, new_master);
                }
                spin_unlock(&tmp->spinlock);
        }

        /* now add a migration mle to the tail of the list */
        dlm_init_mle(mle, DLM_MLE_MIGRATION, dlm, res, name, namelen);
        mle->new_master = new_master;
        /* the new master will be sending an assert master for this.
         * at that point we will get the refmap reference */
        mle->master = master;
        /* do this for consistency with other mle types */
        set_bit(new_master, mle->maybe_map);
        list_add(&mle->list, &dlm->master_list);

        return ret;
}


void dlm_clean_master_list(struct dlm_ctxt *dlm, u8 dead_node)
{
        struct dlm_master_list_entry *mle, *next;
        struct dlm_lock_resource *res;
        unsigned int hash;

        mlog_entry("dlm=%s, dead node=%u\n", dlm->name, dead_node);
top:
        assert_spin_locked(&dlm->spinlock);

        /* clean the master list */
        spin_lock(&dlm->master_lock);
        list_for_each_entry_safe(mle, next, &dlm->master_list, list) {
                BUG_ON(mle->type != DLM_MLE_BLOCK &&
                       mle->type != DLM_MLE_MASTER &&
                       mle->type != DLM_MLE_MIGRATION);

                /* MASTER mles are initiated locally.  the waiting
                 * process will notice the node map change
                 * shortly.  let that happen as normal. */
                if (mle->type == DLM_MLE_MASTER)
                        continue;


                /* BLOCK mles are initiated by other nodes.
                 * need to clean up if the dead node would have
                 * been the master. */
                if (mle->type == DLM_MLE_BLOCK) {
                        int bit;

                        spin_lock(&mle->spinlock);
                        bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
                        if (bit != dead_node) {
                                mlog(0, "mle found, but dead node %u would "
                                     "not have been master\n", dead_node);
                                spin_unlock(&mle->spinlock);
                        } else {
                                /* must drop the refcount by one since the
                                 * assert_master will never arrive.  this
                                 * may result in the mle being unlinked and
                                 * freed, but there may still be a process
                                 * waiting in the dlmlock path which is fine. */
                                mlog(0, "node %u was expected master\n",
                                     dead_node);
                                atomic_set(&mle->woken, 1);
                                spin_unlock(&mle->spinlock);
                                wake_up(&mle->wq);
                                /* do not need events any longer, so detach 
                                 * from heartbeat */
                                __dlm_mle_detach_hb_events(dlm, mle);
                                __dlm_put_mle(mle);
                        }
                        continue;
                }

                /* everything else is a MIGRATION mle */

                /* the rule for MIGRATION mles is that the master
                 * becomes UNKNOWN if *either* the original or
                 * the new master dies.  all UNKNOWN lockreses
                 * are sent to whichever node becomes the recovery
                 * master.  the new master is responsible for
                 * determining if there is still a master for
                 * this lockres, or if he needs to take over
                 * mastery.  either way, this node should expect
                 * another message to resolve this. */
                if (mle->master != dead_node &&
                    mle->new_master != dead_node)
                        continue;

                /* if we have reached this point, this mle needs to
                 * be removed from the list and freed. */

                /* remove from the list early.  NOTE: unlinking
                 * list_head while in list_for_each_safe */
                __dlm_mle_detach_hb_events(dlm, mle);
                spin_lock(&mle->spinlock);
                list_del_init(&mle->list);
                atomic_set(&mle->woken, 1);
                spin_unlock(&mle->spinlock);
                wake_up(&mle->wq);

                mlog(0, "%s: node %u died during migration from "
                     "%u to %u!\n", dlm->name, dead_node,
                     mle->master, mle->new_master);
                /* if there is a lockres associated with this
                 * mle, find it and set its owner to UNKNOWN */
                hash = dlm_lockid_hash(mle->u.name.name, mle->u.name.len);
                res = __dlm_lookup_lockres(dlm, mle->u.name.name,
                                           mle->u.name.len, hash);
                if (res) {
                        /* unfortunately if we hit this rare case, our
                         * lock ordering is messed.  we need to drop
                         * the master lock so that we can take the
                         * lockres lock, meaning that we will have to
                         * restart from the head of list. */
                        spin_unlock(&dlm->master_lock);

                        /* move lockres onto recovery list */
                        spin_lock(&res->spinlock);
                        dlm_set_lockres_owner(dlm, res,
                                        DLM_LOCK_RES_OWNER_UNKNOWN);
                        dlm_move_lockres_to_recovery_list(dlm, res);
                        spin_unlock(&res->spinlock);
                        dlm_lockres_put(res);

                        /* about to get rid of mle, detach from heartbeat */
                        __dlm_mle_detach_hb_events(dlm, mle);

                        /* dump the mle */
                        spin_lock(&dlm->master_lock);
                        __dlm_put_mle(mle);
                        spin_unlock(&dlm->master_lock);

                        /* restart */
                        goto top;
                }

                /* this may be the last reference */
                __dlm_put_mle(mle);
        }
        spin_unlock(&dlm->master_lock);
}


int dlm_finish_migration(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
                         u8 old_master)
{
        struct dlm_node_iter iter;
        int ret = 0;

        spin_lock(&dlm->spinlock);
        dlm_node_iter_init(dlm->domain_map, &iter);
        clear_bit(old_master, iter.node_map);
        clear_bit(dlm->node_num, iter.node_map);
        spin_unlock(&dlm->spinlock);

        /* ownership of the lockres is changing.  account for the
         * mastery reference here since old_master will briefly have
         * a reference after the migration completes */
        spin_lock(&res->spinlock);
        dlm_lockres_set_refmap_bit(old_master, res);
        spin_unlock(&res->spinlock);

        mlog(0, "now time to do a migrate request to other nodes\n");
        ret = dlm_do_migrate_request(dlm, res, old_master,
                                     dlm->node_num, &iter);
        if (ret < 0) {
                mlog_errno(ret);
                goto leave;
        }

        mlog(0, "doing assert master of %.*s to all except the original node\n",
             res->lockname.len, res->lockname.name);
        /* this call now finishes out the nodemap
         * even if one or more nodes die */
        ret = dlm_do_assert_master(dlm, res, iter.node_map,
                                   DLM_ASSERT_MASTER_FINISH_MIGRATION);
        if (ret < 0) {
                /* no longer need to retry.  all living nodes contacted. */
                mlog_errno(ret);
                ret = 0;
        }

        memset(iter.node_map, 0, sizeof(iter.node_map));
        set_bit(old_master, iter.node_map);
        mlog(0, "doing assert master of %.*s back to %u\n",
             res->lockname.len, res->lockname.name, old_master);
        ret = dlm_do_assert_master(dlm, res, iter.node_map,
                                   DLM_ASSERT_MASTER_FINISH_MIGRATION);
        if (ret < 0) {
                mlog(0, "assert master to original master failed "
                     "with %d.\n", ret);
                /* the only nonzero status here would be because of
                 * a dead original node.  we're done. */
                ret = 0;
        }

        /* all done, set the owner, clear the flag */
        spin_lock(&res->spinlock);
        dlm_set_lockres_owner(dlm, res, dlm->node_num);
        res->state &= ~DLM_LOCK_RES_MIGRATING;
        spin_unlock(&res->spinlock);
        /* re-dirty it on the new master */
        dlm_kick_thread(dlm, res);
        wake_up(&res->wq);
leave:
        return ret;
}

/*
 * LOCKRES AST REFCOUNT
 * this is integral to migration
 */

/* for future intent to call an ast, reserve one ahead of time.
 * this should be called only after waiting on the lockres
 * with dlm_wait_on_lockres, and while still holding the
 * spinlock after the call. */
void __dlm_lockres_reserve_ast(struct dlm_lock_resource *res)
{
        assert_spin_locked(&res->spinlock);
        if (res->state & DLM_LOCK_RES_MIGRATING) {
                __dlm_print_one_lock_resource(res);
        }
        BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);

        atomic_inc(&res->asts_reserved);
}

/*
 * used to drop the reserved ast, either because it went unused,
 * or because the ast/bast was actually called.
 *
 * also, if there is a pending migration on this lockres,
 * and this was the last pending ast on the lockres,
 * atomically set the MIGRATING flag before we drop the lock.
 * this is how we ensure that migration can proceed with no
 * asts in progress.  note that it is ok if the state of the
 * queues is such that a lock should be granted in the future
 * or that a bast should be fired, because the new master will
 * shuffle the lists on this lockres as soon as it is migrated.
 */
void dlm_lockres_release_ast(struct dlm_ctxt *dlm,
                             struct dlm_lock_resource *res)
{
        if (!atomic_dec_and_lock(&res->asts_reserved, &res->spinlock))
                return;

        if (!res->migration_pending) {
                spin_unlock(&res->spinlock);
                return;
        }

        BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);
        res->migration_pending = 0;
        res->state |= DLM_LOCK_RES_MIGRATING;
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);
        wake_up(&dlm->migration_wq);
}