CAPI: Rework application locking

Drop the application rw-lock in favour of RCU. This synchronizes
capi20_release against capi_ctr_handle_message which may dereference an
application from (soft-)IRQ context. Any other access to the application
list is now protected by the capi_controller_lock as well. This also
allows to safely inspect applications for /proc dumping by holding
capi_controller_lock.

At this chance, drop some useless release_in_progress checks where we
obtained the application pointer from the list (which becomes NULL on
release_in_progress).

Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c
index a99f7e3..0b4c8a7 100644 (file)
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -34,6 +34,7 @@
 #include <linux/b1lli.h>
 #endif
 #include <linux/mutex.h>
+#include <linux/rcupdate.h>
 
 static int showcapimsgs = 0;
 
@@ -64,8 +65,6 @@ DEFINE_MUTEX(capi_drivers_lock);
 struct capi_ctr *capi_controller[CAPI_MAXCONTR];
 DEFINE_MUTEX(capi_controller_lock);
 
-static DEFINE_RWLOCK(application_lock);
-
 struct capi20_appl *capi_applications[CAPI_MAXAPPL];
 
 static int ncontrollers;
@@ -103,7 +102,7 @@ static inline struct capi20_appl *get_capi_appl_by_nr(u16 applid)
        if (applid - 1 >= CAPI_MAXAPPL)
                return NULL;
 
-       return capi_applications[applid - 1];
+       return rcu_dereference(capi_applications[applid - 1]);
 }
 
 /* -------- util functions ------------------------------------ */
@@ -186,7 +185,7 @@ static void notify_up(u32 contr)
 
                for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
                        ap = get_capi_appl_by_nr(applid);
-                       if (!ap || ap->release_in_progress)
+                       if (!ap)
                                continue;
                        register_appl(ctr, applid, &ap->rparam);
                }
@@ -216,7 +215,7 @@ static void ctr_down(struct capi_ctr *ctr, int new_state)
 
        for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
                ap = get_capi_appl_by_nr(applid);
-               if (ap && !ap->release_in_progress)
+               if (ap)
                        capi_ctr_put(ctr);
        }
 
@@ -336,7 +335,6 @@ void capi_ctr_handle_message(struct capi_ctr *ctr, u16 appl,
        struct capi20_appl *ap;
        int showctl = 0;
        u8 cmd, subcmd;
-       unsigned long flags;
        _cdebbuf *cdb;
 
        if (ctr->state != CAPI_CTR_RUNNING) {
@@ -384,10 +382,10 @@ void capi_ctr_handle_message(struct capi_ctr *ctr, u16 appl,
 
        }
 
-       read_lock_irqsave(&application_lock, flags);
+       rcu_read_lock();
        ap = get_capi_appl_by_nr(CAPIMSG_APPID(skb->data));
-       if ((!ap) || (ap->release_in_progress)) {
-               read_unlock_irqrestore(&application_lock, flags);
+       if (!ap) {
+               rcu_read_unlock();
                cdb = capi_message2str(skb->data);
                if (cdb) {
                        printk(KERN_ERR "kcapi: handle_message: applid %d state released (%s)\n",
@@ -401,7 +399,7 @@ void capi_ctr_handle_message(struct capi_ctr *ctr, u16 appl,
        }
        skb_queue_tail(&ap->recv_queue, skb);
        schedule_work(&ap->recv_work);
-       read_unlock_irqrestore(&application_lock, flags);
+       rcu_read_unlock();
 
        return;
 
@@ -656,40 +654,35 @@ u16 capi20_register(struct capi20_appl *ap)
 {
        int i;
        u16 applid;
-       unsigned long flags;
 
        DBG("");
 
        if (ap->rparam.datablklen < 128)
                return CAPI_LOGBLKSIZETOSMALL;
 
-       write_lock_irqsave(&application_lock, flags);
+       ap->nrecvctlpkt = 0;
+       ap->nrecvdatapkt = 0;
+       ap->nsentctlpkt = 0;
+       ap->nsentdatapkt = 0;
+       mutex_init(&ap->recv_mtx);
+       skb_queue_head_init(&ap->recv_queue);
+       INIT_WORK(&ap->recv_work, recv_handler);
+       ap->release_in_progress = 0;
+
+       mutex_lock(&capi_controller_lock);
 
        for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
                if (capi_applications[applid - 1] == NULL)
                        break;
        }
        if (applid > CAPI_MAXAPPL) {
-               write_unlock_irqrestore(&application_lock, flags);
+               mutex_unlock(&capi_controller_lock);
                return CAPI_TOOMANYAPPLS;
        }
 
        ap->applid = applid;
        capi_applications[applid - 1] = ap;
 
-       ap->nrecvctlpkt = 0;
-       ap->nrecvdatapkt = 0;
-       ap->nsentctlpkt = 0;
-       ap->nsentdatapkt = 0;
-       mutex_init(&ap->recv_mtx);
-       skb_queue_head_init(&ap->recv_queue);
-       INIT_WORK(&ap->recv_work, recv_handler);
-       ap->release_in_progress = 0;
-
-       write_unlock_irqrestore(&application_lock, flags);
-       
-       mutex_lock(&capi_controller_lock);
-
        for (i = 0; i < CAPI_MAXCONTR; i++) {
                if (!capi_controller[i] ||
                    capi_controller[i]->state != CAPI_CTR_RUNNING)
@@ -721,16 +714,15 @@ EXPORT_SYMBOL(capi20_register);
 u16 capi20_release(struct capi20_appl *ap)
 {
        int i;
-       unsigned long flags;
 
        DBG("applid %#x", ap->applid);
 
-       write_lock_irqsave(&application_lock, flags);
+       mutex_lock(&capi_controller_lock);
+
        ap->release_in_progress = 1;
        capi_applications[ap->applid - 1] = NULL;
-       write_unlock_irqrestore(&application_lock, flags);
 
-       mutex_lock(&capi_controller_lock);
+       synchronize_rcu();
 
        for (i = 0; i < CAPI_MAXCONTR; i++) {
                if (!capi_controller[i] ||

diff --git a/drivers/isdn/capi/kcapi_proc.c b/drivers/isdn/capi/kcapi_proc.c
index 3e6e17a..ea2dff6 100644 (file)
--- a/drivers/isdn/capi/kcapi_proc.c
+++ b/drivers/isdn/capi/kcapi_proc.c
@@ -139,9 +139,11 @@ static const struct file_operations proc_contrstats_ops = {
 //      applid nrecvctlpkt nrecvdatapkt nsentctlpkt nsentdatapkt
 // ---------------------------------------------------------------------------
 
-static void *
-applications_start(struct seq_file *seq, loff_t *pos)
+static void *applications_start(struct seq_file *seq, loff_t *pos)
+       __acquires(capi_controller_lock)
 {
+       mutex_lock(&capi_controller_lock);
+
        if (*pos < CAPI_MAXAPPL)
                return &capi_applications[*pos];
 
@@ -158,9 +160,10 @@ applications_next(struct seq_file *seq, void *v, loff_t *pos)
        return NULL;
 }
 
-static void
-applications_stop(struct seq_file *seq, void *v)
+static void applications_stop(struct seq_file *seq, void *v)
+       __releases(capi_controller_lock)
 {
+       mutex_unlock(&capi_controller_lock);
 }
 
 static int