[3.16.y-ckt stable] Patch "dm thin: fix a race in thin_dtr" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    dm thin: fix a race in thin_dtr

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From d0b43a0878dd723adaa4b3453564127a3763e963 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka at redhat.com>
Date: Wed, 5 Nov 2014 17:00:13 -0500
Subject: 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 at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at 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