dm thin: fix a race in thin_dtr

commit 17181fb7a0c3a279196c0eeb2caba65a1519614b upstream.

As long as struct thin_c is in the list, anyone can grab a reference of
it.  Consequently, we must wait for the reference count to drop to zero
*after* we remove the structure from the list, not before.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index df898e0db4195ff4dd339ee462f2da40fef0deab..6f75083a81cc0057713f8e1dd0d408a195246a55 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3183,14 +3183,14 @@ static void thin_dtr(struct dm_target *ti)
        struct thin_c *tc = ti->private;
        unsigned long flags;
 
-       thin_put(tc);
-       wait_for_completion(&tc->can_destroy);
-
        spin_lock_irqsave(&tc->pool->lock, flags);
        list_del_rcu(&tc->list);
        spin_unlock_irqrestore(&tc->pool->lock, flags);
        synchronize_rcu();
 
+       thin_put(tc);
+       wait_for_completion(&tc->can_destroy);
+
        mutex_lock(&dm_thin_pool_table.mutex);
 
        __pool_dec(tc->pool);