From: Mikulas Patocka <mpatocka@redhat.com>
Date: Wed, 5 Nov 2014 22:00:13 +0000 (-0500)
Subject: dm thin: fix a race in thin_dtr
X-Git-Tag: v3.17.8~47
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1a6f39233d864d62c6f26cda68df404d814baf4c;p=thirdparty%2Fkernel%2Fstable.git

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 3ae87a39e4c9e..aae19133cfac0 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3266,14 +3266,14 @@ 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);