dlm: fix locking of lockspace list in dlm_scand
[safe/jmp/linux-2.6] / fs / dlm / user.c
index d378b7f..81627b5 100644 (file)
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2006 Red Hat, Inc.  All rights reserved.
+ * Copyright (C) 2006-2008 Red Hat, Inc.  All rights reserved.
  *
  * This copyrighted material is made available to anyone wishing to use,
  * modify, copy, or redistribute it subject to the terms and conditions
@@ -15,6 +15,7 @@
 #include <linux/poll.h>
 #include <linux/signal.h>
 #include <linux/spinlock.h>
+#include <linux/smp_lock.h>
 #include <linux/dlm.h>
 #include <linux/dlm_device.h>
 
 #include "lockspace.h"
 #include "lock.h"
 #include "lvb_table.h"
+#include "user.h"
 
-static const char *name_prefix="dlm";
-static struct miscdevice ctl_device;
-static struct file_operations device_fops;
+static const char name_prefix[] = "dlm";
+static const struct file_operations device_fops;
+static atomic_t dlm_monitor_opened;
+static int dlm_monitor_unused = 1;
 
 #ifdef CONFIG_COMPAT
 
 struct dlm_lock_params32 {
        __u8 mode;
        __u8 namelen;
-       __u16 flags;
+       __u16 unused;
+       __u32 flags;
        __u32 lkid;
        __u32 parent;
-
+       __u64 xid;
+       __u64 timeout;
        __u32 castparam;
        __u32 castaddr;
        __u32 bastparam;
        __u32 bastaddr;
        __u32 lksb;
-
        char lvb[DLM_USER_LVB_LEN];
        char name[0];
 };
@@ -55,6 +59,7 @@ struct dlm_write_request32 {
        union  {
                struct dlm_lock_params32 lock;
                struct dlm_lspace_params lspace;
+               struct dlm_purge_params purge;
        } i;
 };
 
@@ -66,6 +71,7 @@ struct dlm_lksb32 {
 };
 
 struct dlm_lock_result32 {
+       __u32 version[3];
        __u32 length;
        __u32 user_astaddr;
        __u32 user_astparam;
@@ -78,7 +84,8 @@ struct dlm_lock_result32 {
 };
 
 static void compat_input(struct dlm_write_request *kb,
-                        struct dlm_write_request32 *kb32)
+                        struct dlm_write_request32 *kb32,
+                        size_t count)
 {
        kb->version[0] = kb32->version[0];
        kb->version[1] = kb32->version[1];
@@ -90,28 +97,37 @@ static void compat_input(struct dlm_write_request *kb,
            kb->cmd == DLM_USER_REMOVE_LOCKSPACE) {
                kb->i.lspace.flags = kb32->i.lspace.flags;
                kb->i.lspace.minor = kb32->i.lspace.minor;
-               strcpy(kb->i.lspace.name, kb32->i.lspace.name);
+               memcpy(kb->i.lspace.name, kb32->i.lspace.name, count -
+                       offsetof(struct dlm_write_request32, i.lspace.name));
+       } else if (kb->cmd == DLM_USER_PURGE) {
+               kb->i.purge.nodeid = kb32->i.purge.nodeid;
+               kb->i.purge.pid = kb32->i.purge.pid;
        } else {
                kb->i.lock.mode = kb32->i.lock.mode;
                kb->i.lock.namelen = kb32->i.lock.namelen;
                kb->i.lock.flags = kb32->i.lock.flags;
                kb->i.lock.lkid = kb32->i.lock.lkid;
                kb->i.lock.parent = kb32->i.lock.parent;
+               kb->i.lock.xid = kb32->i.lock.xid;
+               kb->i.lock.timeout = kb32->i.lock.timeout;
                kb->i.lock.castparam = (void *)(long)kb32->i.lock.castparam;
                kb->i.lock.castaddr = (void *)(long)kb32->i.lock.castaddr;
                kb->i.lock.bastparam = (void *)(long)kb32->i.lock.bastparam;
                kb->i.lock.bastaddr = (void *)(long)kb32->i.lock.bastaddr;
                kb->i.lock.lksb = (void *)(long)kb32->i.lock.lksb;
                memcpy(kb->i.lock.lvb, kb32->i.lock.lvb, DLM_USER_LVB_LEN);
-               memcpy(kb->i.lock.name, kb32->i.lock.name, kb->i.lock.namelen);
+               memcpy(kb->i.lock.name, kb32->i.lock.name, count -
+                       offsetof(struct dlm_write_request32, i.lock.name));
        }
 }
 
 static void compat_output(struct dlm_lock_result *res,
                          struct dlm_lock_result32 *res32)
 {
-       res32->length = res->length - (sizeof(struct dlm_lock_result) -
-                                      sizeof(struct dlm_lock_result32));
+       res32->version[0] = res->version[0];
+       res32->version[1] = res->version[1];
+       res32->version[2] = res->version[2];
+
        res32->user_astaddr = (__u32)(long)res->user_astaddr;
        res32->user_astparam = (__u32)(long)res->user_astparam;
        res32->user_lksb = (__u32)(long)res->user_lksb;
@@ -127,66 +143,87 @@ static void compat_output(struct dlm_lock_result *res,
 }
 #endif
 
+/* Figure out if this lock is at the end of its life and no longer
+   available for the application to use.  The lkb still exists until
+   the final ast is read.  A lock becomes EOL in three situations:
+     1. a noqueue request fails with EAGAIN
+     2. an unlock completes with EUNLOCK
+     3. a cancel of a waiting request completes with ECANCEL/EDEADLK
+   An EOL lock needs to be removed from the process's list of locks.
+   And we can't allow any new operation on an EOL lock.  This is
+   not related to the lifetime of the lkb struct which is managed
+   entirely by refcount. */
+
+static int lkb_is_endoflife(struct dlm_lkb *lkb, int sb_status, int type)
+{
+       switch (sb_status) {
+       case -DLM_EUNLOCK:
+               return 1;
+       case -DLM_ECANCEL:
+       case -ETIMEDOUT:
+       case -EDEADLK:
+               if (lkb->lkb_grmode == DLM_LOCK_IV)
+                       return 1;
+               break;
+       case -EAGAIN:
+               if (type == AST_COMP && lkb->lkb_grmode == DLM_LOCK_IV)
+                       return 1;
+               break;
+       }
+       return 0;
+}
+
+/* we could possibly check if the cancel of an orphan has resulted in the lkb
+   being removed and then remove that lkb from the orphans list and free it */
 
 void dlm_user_add_ast(struct dlm_lkb *lkb, int type)
 {
        struct dlm_ls *ls;
        struct dlm_user_args *ua;
        struct dlm_user_proc *proc;
-       int remove_ownqueue = 0;
+       int eol = 0, ast_type;
 
-       /* dlm_clear_proc_locks() sets ORPHAN/DEAD flag on each
-          lkb before dealing with it.  We need to check this
-          flag before taking ls_clear_proc_locks mutex because if
-          it's set, dlm_clear_proc_locks() holds the mutex. */
-
-       if (lkb->lkb_flags & (DLM_IFL_ORPHAN | DLM_IFL_DEAD)) {
-               /* log_print("user_add_ast skip1 %x", lkb->lkb_flags); */
+       if (lkb->lkb_flags & (DLM_IFL_ORPHAN | DLM_IFL_DEAD))
                return;
-       }
 
        ls = lkb->lkb_resource->res_ls;
        mutex_lock(&ls->ls_clear_proc_locks);
 
        /* If ORPHAN/DEAD flag is set, it means the process is dead so an ast
           can't be delivered.  For ORPHAN's, dlm_clear_proc_locks() freed
-          lkb->ua so we can't try to use it. */
+          lkb->ua so we can't try to use it.  This second check is necessary
+          for cases where a completion ast is received for an operation that
+          began before clear_proc_locks did its cancel/unlock. */
 
-       if (lkb->lkb_flags & (DLM_IFL_ORPHAN | DLM_IFL_DEAD)) {
-               /* log_print("user_add_ast skip2 %x", lkb->lkb_flags); */
+       if (lkb->lkb_flags & (DLM_IFL_ORPHAN | DLM_IFL_DEAD))
                goto out;
-       }
 
-       DLM_ASSERT(lkb->lkb_astparam, dlm_print_lkb(lkb););
-       ua = (struct dlm_user_args *)lkb->lkb_astparam;
+       DLM_ASSERT(lkb->lkb_ua, dlm_print_lkb(lkb););
+       ua = lkb->lkb_ua;
        proc = ua->proc;
 
        if (type == AST_BAST && ua->bastaddr == NULL)
                goto out;
 
        spin_lock(&proc->asts_spin);
-       if (!(lkb->lkb_ast_type & (AST_COMP | AST_BAST))) {
+
+       ast_type = lkb->lkb_ast_type;
+       lkb->lkb_ast_type |= type;
+
+       if (!ast_type) {
                kref_get(&lkb->lkb_ref);
                list_add_tail(&lkb->lkb_astqueue, &proc->asts);
-               lkb->lkb_ast_type |= type;
                wake_up_interruptible(&proc->wait);
        }
+       if (type == AST_COMP && (ast_type & AST_COMP))
+               log_debug(ls, "ast overlap %x status %x %x",
+                         lkb->lkb_id, ua->lksb.sb_status, lkb->lkb_flags);
 
-       /* noqueue requests that fail may need to be removed from the
-          proc's locks list, there should be a better way of detecting
-          this situation than checking all these things... */
-
-       if (type == AST_COMP && lkb->lkb_grmode == DLM_LOCK_IV &&
-           ua->lksb.sb_status == -EAGAIN && !list_empty(&lkb->lkb_ownqueue))
-               remove_ownqueue = 1;
-
-       /* unlocks or cancels of waiting requests need to be removed from the
-          proc's unlocking list, again there must be a better way...  */
-
-       if (ua->lksb.sb_status == -DLM_EUNLOCK ||
-           (ua->lksb.sb_status == -DLM_ECANCEL &&
-            lkb->lkb_grmode == DLM_LOCK_IV))
-               remove_ownqueue = 1;
+       eol = lkb_is_endoflife(lkb, ua->lksb.sb_status, type);
+       if (eol) {
+               lkb->lkb_ast_type &= ~AST_BAST;
+               lkb->lkb_flags |= DLM_IFL_ENDOFLIFE;
+       }
 
        /* We want to copy the lvb to userspace when the completion
           ast is read if the status is 0, the lock has an lvb and
@@ -203,11 +240,13 @@ void dlm_user_add_ast(struct dlm_lkb *lkb, int type)
 
        spin_unlock(&proc->asts_spin);
 
-       if (remove_ownqueue) {
-               spin_lock(&ua->proc->locks_spin);
-               list_del_init(&lkb->lkb_ownqueue);
-               spin_unlock(&ua->proc->locks_spin);
-               dlm_put_lkb(lkb);
+       if (eol) {
+               spin_lock(&proc->locks_spin);
+               if (!list_empty(&lkb->lkb_ownqueue)) {
+                       list_del_init(&lkb->lkb_ownqueue);
+                       dlm_put_lkb(lkb);
+               }
+               spin_unlock(&proc->locks_spin);
        }
  out:
        mutex_unlock(&ls->ls_clear_proc_locks);
@@ -238,16 +277,18 @@ static int device_user_lock(struct dlm_user_proc *proc,
        ua->castaddr = params->castaddr;
        ua->bastparam = params->bastparam;
        ua->bastaddr = params->bastaddr;
+       ua->xid = params->xid;
 
        if (params->flags & DLM_LKF_CONVERT)
                error = dlm_user_convert(ls, ua,
                                         params->mode, params->flags,
-                                        params->lkid, params->lvb);
+                                        params->lkid, params->lvb,
+                                        (unsigned long) params->timeout);
        else {
                error = dlm_user_request(ls, ua,
                                         params->mode, params->flags,
                                         params->name, params->namelen,
-                                        params->parent);
+                                        (unsigned long) params->timeout);
                if (!error)
                        error = ua->lksb.sb_lkid;
        }
@@ -285,47 +326,108 @@ static int device_user_unlock(struct dlm_user_proc *proc,
        return error;
 }
 
-static int device_create_lockspace(struct dlm_lspace_params *params)
+static int device_user_deadlock(struct dlm_user_proc *proc,
+                               struct dlm_lock_params *params)
 {
-       dlm_lockspace_t *lockspace;
        struct dlm_ls *ls;
-       int error, len;
-
-       if (!capable(CAP_SYS_ADMIN))
-               return -EPERM;
-
-       error = dlm_new_lockspace(params->name, strlen(params->name),
-                                 &lockspace, 0, DLM_USER_LVB_LEN);
-       if (error)
-               return error;
+       int error;
 
-       ls = dlm_find_lockspace_local(lockspace);
+       ls = dlm_find_lockspace_local(proc->lockspace);
        if (!ls)
                return -ENOENT;
 
+       error = dlm_user_deadlock(ls, params->flags, params->lkid);
+
+       dlm_put_lockspace(ls);
+       return error;
+}
+
+static int dlm_device_register(struct dlm_ls *ls, char *name)
+{
+       int error, len;
+
+       /* The device is already registered.  This happens when the
+          lockspace is created multiple times from userspace. */
+       if (ls->ls_device.name)
+               return 0;
+
        error = -ENOMEM;
-       len = strlen(params->name) + strlen(name_prefix) + 2;
+       len = strlen(name) + strlen(name_prefix) + 2;
        ls->ls_device.name = kzalloc(len, GFP_KERNEL);
        if (!ls->ls_device.name)
                goto fail;
+
        snprintf((char *)ls->ls_device.name, len, "%s_%s", name_prefix,
-                params->name);
+                name);
        ls->ls_device.fops = &device_fops;
        ls->ls_device.minor = MISC_DYNAMIC_MINOR;
 
        error = misc_register(&ls->ls_device);
        if (error) {
                kfree(ls->ls_device.name);
-               goto fail;
        }
+fail:
+       return error;
+}
+
+int dlm_device_deregister(struct dlm_ls *ls)
+{
+       int error;
+
+       /* The device is not registered.  This happens when the lockspace
+          was never used from userspace, or when device_create_lockspace()
+          calls dlm_release_lockspace() after the register fails. */
+       if (!ls->ls_device.name)
+               return 0;
+
+       error = misc_deregister(&ls->ls_device);
+       if (!error)
+               kfree(ls->ls_device.name);
+       return error;
+}
+
+static int device_user_purge(struct dlm_user_proc *proc,
+                            struct dlm_purge_params *params)
+{
+       struct dlm_ls *ls;
+       int error;
+
+       ls = dlm_find_lockspace_local(proc->lockspace);
+       if (!ls)
+               return -ENOENT;
+
+       error = dlm_user_purge(ls, proc, params->nodeid, params->pid);
 
-       error = ls->ls_device.minor;
        dlm_put_lockspace(ls);
        return error;
+}
+
+static int device_create_lockspace(struct dlm_lspace_params *params)
+{
+       dlm_lockspace_t *lockspace;
+       struct dlm_ls *ls;
+       int error;
+
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
 
- fail:
+       error = dlm_new_lockspace(params->name, strlen(params->name),
+                                 &lockspace, params->flags, DLM_USER_LVB_LEN);
+       if (error)
+               return error;
+
+       ls = dlm_find_lockspace_local(lockspace);
+       if (!ls)
+               return -ENOENT;
+
+       error = dlm_device_register(ls, params->name);
        dlm_put_lockspace(ls);
-       dlm_release_lockspace(lockspace, 0);
+
+       if (error)
+               dlm_release_lockspace(lockspace, 0);
+       else
+               error = ls->ls_device.minor;
+
        return error;
 }
 
@@ -342,25 +444,22 @@ static int device_remove_lockspace(struct dlm_lspace_params *params)
        if (!ls)
                return -ENOENT;
 
-       error = misc_deregister(&ls->ls_device);
-       if (error) {
-               dlm_put_lockspace(ls);
-               goto out;
-       }
-       kfree(ls->ls_device.name);
-
        if (params->flags & DLM_USER_LSFLG_FORCEFREE)
                force = 2;
 
        lockspace = ls->ls_local_handle;
+       dlm_put_lockspace(ls);
 
-       /* dlm_release_lockspace waits for references to go to zero,
-          so all processes will need to close their device for the ls
-          before the release will procede */
+       /* The final dlm_release_lockspace waits for references to go to
+          zero, so all processes will need to close their device for the
+          ls before the release will proceed.  release also calls the
+          device_deregister above.  Converting a positive return value
+          from release to zero means that userspace won't know when its
+          release was the final one, but it shouldn't need to know. */
 
-       dlm_put_lockspace(ls);
        error = dlm_release_lockspace(lockspace, force);
- out:
+       if (error > 0)
+               error = 0;
        return error;
 }
 
@@ -374,7 +473,7 @@ static int check_version(struct dlm_write_request *req)
                printk(KERN_DEBUG "dlm: process %s (%d) version mismatch "
                       "user (%d.%d.%d) kernel (%d.%d.%d)\n",
                       current->comm,
-                      current->pid,
+                      task_pid_nr(current),
                       req->version[0],
                       req->version[1],
                       req->version[2],
@@ -422,7 +521,7 @@ static ssize_t device_write(struct file *file, const char __user *buf,
 #endif
                return -EINVAL;
 
-       kbuf = kmalloc(count, GFP_KERNEL);
+       kbuf = kzalloc(count + 1, GFP_KERNEL);
        if (!kbuf)
                return -ENOMEM;
 
@@ -440,22 +539,26 @@ static ssize_t device_write(struct file *file, const char __user *buf,
        if (!kbuf->is64bit) {
                struct dlm_write_request32 *k32buf;
                k32buf = (struct dlm_write_request32 *)kbuf;
-               kbuf = kmalloc(count + (sizeof(struct dlm_write_request) -
+               kbuf = kmalloc(count + 1 + (sizeof(struct dlm_write_request) -
                               sizeof(struct dlm_write_request32)), GFP_KERNEL);
-               if (!kbuf)
+               if (!kbuf) {
+                       kfree(k32buf);
                        return -ENOMEM;
+               }
 
                if (proc)
                        set_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags);
-               compat_input(kbuf, k32buf);
+               compat_input(kbuf, k32buf, count + 1);
                kfree(k32buf);
        }
 #endif
 
        /* do we really need this? can a write happen after a close? */
        if ((kbuf->cmd == DLM_USER_LOCK || kbuf->cmd == DLM_USER_UNLOCK) &&
-           test_bit(DLM_PROC_FLAGS_CLOSING, &proc->flags))
-               return -EINVAL;
+           (proc && test_bit(DLM_PROC_FLAGS_CLOSING, &proc->flags))) {
+               error = -EINVAL;
+               goto out_free;
+       }
 
        sigfillset(&allsigs);
        sigprocmask(SIG_BLOCK, &allsigs, &tmpsig);
@@ -480,6 +583,14 @@ static ssize_t device_write(struct file *file, const char __user *buf,
                error = device_user_unlock(proc, &kbuf->i.lock);
                break;
 
+       case DLM_USER_DEADLOCK:
+               if (!proc) {
+                       log_print("no locking on control device");
+                       goto out_sig;
+               }
+               error = device_user_deadlock(proc, &kbuf->i.lock);
+               break;
+
        case DLM_USER_CREATE_LOCKSPACE:
                if (proc) {
                        log_print("create/remove only on control device");
@@ -496,6 +607,14 @@ static ssize_t device_write(struct file *file, const char __user *buf,
                error = device_remove_lockspace(&kbuf->i.lspace);
                break;
 
+       case DLM_USER_PURGE:
+               if (!proc) {
+                       log_print("no locking on control device");
+                       goto out_sig;
+               }
+               error = device_user_purge(proc, &kbuf->i.purge);
+               break;
+
        default:
                log_print("Unknown command passed to DLM device : %d\n",
                          kbuf->cmd);
@@ -518,13 +637,17 @@ static int device_open(struct inode *inode, struct file *file)
        struct dlm_user_proc *proc;
        struct dlm_ls *ls;
 
+       lock_kernel();
        ls = dlm_find_lockspace_device(iminor(inode));
-       if (!ls)
+       if (!ls) {
+               unlock_kernel();
                return -ENOENT;
+       }
 
        proc = kzalloc(sizeof(struct dlm_user_proc), GFP_KERNEL);
        if (!proc) {
                dlm_put_lockspace(ls);
+               unlock_kernel();
                return -ENOMEM;
        }
 
@@ -536,6 +659,7 @@ static int device_open(struct inode *inode, struct file *file)
        spin_lock_init(&proc->locks_spin);
        init_waitqueue_head(&proc->wait);
        file->private_data = proc;
+       unlock_kernel();
 
        return 0;
 }
@@ -589,6 +713,9 @@ static int copy_result_to_user(struct dlm_user_args *ua, int compat, int type,
        int struct_len;
 
        memset(&result, 0, sizeof(struct dlm_lock_result));
+       result.version[0] = DLM_DEVICE_VERSION_MAJOR;
+       result.version[1] = DLM_DEVICE_VERSION_MINOR;
+       result.version[2] = DLM_DEVICE_VERSION_PATCH;
        memcpy(&result.lksb, &ua->lksb, sizeof(struct dlm_lksb));
        result.user_lksb = ua->user_lksb;
 
@@ -647,6 +774,20 @@ static int copy_result_to_user(struct dlm_user_args *ua, int compat, int type,
        return error;
 }
 
+static int copy_version_to_user(char __user *buf, size_t count)
+{
+       struct dlm_device_version ver;
+
+       memset(&ver, 0, sizeof(struct dlm_device_version));
+       ver.version[0] = DLM_DEVICE_VERSION_MAJOR;
+       ver.version[1] = DLM_DEVICE_VERSION_MINOR;
+       ver.version[2] = DLM_DEVICE_VERSION_PATCH;
+
+       if (copy_to_user(buf, &ver, sizeof(struct dlm_device_version)))
+               return -EFAULT;
+       return sizeof(struct dlm_device_version);
+}
+
 /* a read returns a single ast described in a struct dlm_lock_result */
 
 static ssize_t device_read(struct file *file, char __user *buf, size_t count,
@@ -654,10 +795,19 @@ static ssize_t device_read(struct file *file, char __user *buf, size_t count,
 {
        struct dlm_user_proc *proc = file->private_data;
        struct dlm_lkb *lkb;
-       struct dlm_user_args *ua;
        DECLARE_WAITQUEUE(wait, current);
        int error, type=0, bmode=0, removed = 0;
 
+       if (count == sizeof(struct dlm_device_version)) {
+               error = copy_version_to_user(buf, count);
+               return error;
+       }
+
+       if (!proc) {
+               log_print("non-version read from control device %zu", count);
+               return -EINVAL;
+       }
+
 #ifdef CONFIG_COMPAT
        if (count < sizeof(struct dlm_lock_result32))
 #else
@@ -695,11 +845,6 @@ static ssize_t device_read(struct file *file, char __user *buf, size_t count,
                }
        }
 
-       if (list_empty(&proc->asts)) {
-               spin_unlock(&proc->asts_spin);
-               return -EAGAIN;
-       }
-
        /* there may be both completion and blocking asts to return for
           the lkb, don't remove lkb from asts list unless no asts remain */
 
@@ -720,8 +865,7 @@ static ssize_t device_read(struct file *file, char __user *buf, size_t count,
        }
        spin_unlock(&proc->asts_spin);
 
-       ua = (struct dlm_user_args *)lkb->lkb_astparam;
-       error = copy_result_to_user(ua,
+       error = copy_result_to_user(lkb->lkb_ua,
                                test_bit(DLM_PROC_FLAGS_COMPAT, &proc->flags),
                                type, bmode, buf, count);
 
@@ -748,8 +892,29 @@ static unsigned int device_poll(struct file *file, poll_table *wait)
        return 0;
 }
 
+int dlm_user_daemon_available(void)
+{
+       /* dlm_controld hasn't started (or, has started, but not
+          properly populated configfs) */
+
+       if (!dlm_our_nodeid())
+               return 0;
+
+       /* This is to deal with versions of dlm_controld that don't
+          know about the monitor device.  We assume that if the
+          dlm_controld was started (above), but the monitor device
+          was never opened, that it's an old version.  dlm_controld
+          should open the monitor device before populating configfs. */
+
+       if (dlm_monitor_unused)
+               return 1;
+
+       return atomic_read(&dlm_monitor_opened) ? 1 : 0;
+}
+
 static int ctl_device_open(struct inode *inode, struct file *file)
 {
+       cycle_kernel_lock();
        file->private_data = NULL;
        return 0;
 }
@@ -759,7 +924,21 @@ static int ctl_device_close(struct inode *inode, struct file *file)
        return 0;
 }
 
-static struct file_operations device_fops = {
+static int monitor_device_open(struct inode *inode, struct file *file)
+{
+       atomic_inc(&dlm_monitor_opened);
+       dlm_monitor_unused = 0;
+       return 0;
+}
+
+static int monitor_device_close(struct inode *inode, struct file *file)
+{
+       if (atomic_dec_and_test(&dlm_monitor_opened))
+               dlm_stop_lockspaces();
+       return 0;
+}
+
+static const struct file_operations device_fops = {
        .open    = device_open,
        .release = device_close,
        .read    = device_read,
@@ -768,30 +947,56 @@ static struct file_operations device_fops = {
        .owner   = THIS_MODULE,
 };
 
-static struct file_operations ctl_device_fops = {
+static const struct file_operations ctl_device_fops = {
        .open    = ctl_device_open,
        .release = ctl_device_close,
+       .read    = device_read,
        .write   = device_write,
        .owner   = THIS_MODULE,
 };
 
-int dlm_user_init(void)
+static struct miscdevice ctl_device = {
+       .name  = "dlm-control",
+       .fops  = &ctl_device_fops,
+       .minor = MISC_DYNAMIC_MINOR,
+};
+
+static const struct file_operations monitor_device_fops = {
+       .open    = monitor_device_open,
+       .release = monitor_device_close,
+       .owner   = THIS_MODULE,
+};
+
+static struct miscdevice monitor_device = {
+       .name  = "dlm-monitor",
+       .fops  = &monitor_device_fops,
+       .minor = MISC_DYNAMIC_MINOR,
+};
+
+int __init dlm_user_init(void)
 {
        int error;
 
-       ctl_device.name = "dlm-control";
-       ctl_device.fops = &ctl_device_fops;
-       ctl_device.minor = MISC_DYNAMIC_MINOR;
+       atomic_set(&dlm_monitor_opened, 0);
 
        error = misc_register(&ctl_device);
-       if (error)
+       if (error) {
                log_print("misc_register failed for control device");
+               goto out;
+       }
 
+       error = misc_register(&monitor_device);
+       if (error) {
+               log_print("misc_register failed for monitor device");
+               misc_deregister(&ctl_device);
+       }
+ out:
        return error;
 }
 
 void dlm_user_exit(void)
 {
        misc_deregister(&ctl_device);
+       misc_deregister(&monitor_device);
 }