[PATCH 3.16.y-ckt 152/216] dm thin: fix a race in thin_dtr

Luis Henriques
2015-01-12T18:54:07Z

From: Mikulas Patocka <mpatocka@redhat.com>

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>
---
drivers/md/dm-thin.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index df898e0db419..6f75083a81cc 100644
--- 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);
--
2.1.4