dm raid1: fix deadlock when suspending failed device
Takahiro Yasui [Sat, 6 Mar 2010 02:32:35 +0000 (02:32 +0000)]
To prevent deadlock, bios in the hold list should be flushed before
dm_rh_stop_recovery() is called in mirror_suspend().

The recovery can't start because there are pending bios and therefore
dm_rh_stop_recovery deadlocks.

When there are pending bios in the hold list, the recovery waits for
the completion of the bios after recovery_count is acquired.
The recovery_count is released when the recovery finished, however,
the bios in the hold list are processed after dm_rh_stop_recovery() in
mirror_presuspend(). dm_rh_stop_recovery() also acquires recovery_count,
then deadlock occurs.

Signed-off-by: Takahiro Yasui <tyasui@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>

drivers/md/dm-raid1.c

index 6d66ddf..ddda531 100644 (file)
@@ -465,9 +465,17 @@ static void map_region(struct dm_io_region *io, struct mirror *m,
 static void hold_bio(struct mirror_set *ms, struct bio *bio)
 {
        /*
-        * If device is suspended, complete the bio.
+        * Lock is required to avoid race condition during suspend
+        * process.
         */
+       spin_lock_irq(&ms->lock);
+
        if (atomic_read(&ms->suspend)) {
+               spin_unlock_irq(&ms->lock);
+
+               /*
+                * If device is suspended, complete the bio.
+                */
                if (dm_noflush_suspending(ms->ti))
                        bio_endio(bio, DM_ENDIO_REQUEUE);
                else
@@ -478,7 +486,6 @@ static void hold_bio(struct mirror_set *ms, struct bio *bio)
        /*
         * Hold bio until the suspend is complete.
         */
-       spin_lock_irq(&ms->lock);
        bio_list_add(&ms->holds, bio);
        spin_unlock_irq(&ms->lock);
 }
@@ -1261,6 +1268,20 @@ static void mirror_presuspend(struct dm_target *ti)
        atomic_set(&ms->suspend, 1);
 
        /*
+        * Process bios in the hold list to start recovery waiting
+        * for bios in the hold list. After the process, no bio has
+        * a chance to be added in the hold list because ms->suspend
+        * is set.
+        */
+       spin_lock_irq(&ms->lock);
+       holds = ms->holds;
+       bio_list_init(&ms->holds);
+       spin_unlock_irq(&ms->lock);
+
+       while ((bio = bio_list_pop(&holds)))
+               hold_bio(ms, bio);
+
+       /*
         * We must finish up all the work that we've
         * generated (i.e. recovery work).
         */
@@ -1280,22 +1301,6 @@ static void mirror_presuspend(struct dm_target *ti)
         * we know that all of our I/O has been pushed.
         */
        flush_workqueue(ms->kmirrord_wq);
-
-       /*
-        * Now set ms->suspend is set and the workqueue flushed, no more
-        * entries can be added to ms->hold list, so process it.
-        *
-        * Bios can still arrive concurrently with or after this
-        * presuspend function, but they cannot join the hold list
-        * because ms->suspend is set.
-        */
-       spin_lock_irq(&ms->lock);
-       holds = ms->holds;
-       bio_list_init(&ms->holds);
-       spin_unlock_irq(&ms->lock);
-
-       while ((bio = bio_list_pop(&holds)))
-               hold_bio(ms, bio);
 }
 
 static void mirror_postsuspend(struct dm_target *ti)