[PATCH 3.18 30/84] dm thin: fix a race in thin_dtr

From: Greg Kroah-Hartman
Date: Tue Jan 06 2015 - 22:05:49 EST


3.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3266,14 +3266,14 @@ static void thin_dtr(struct dm_target *t
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);


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