linux-kernel - [PATCH 3.16.y-ckt 06/94] dm: fix AB-BA deadlock in __dm

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Message-Id: <1447409428-12178-7-git-send-email-luis.henriques@canonical.com>
Date:	Fri, 13 Nov 2015 10:09:00 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jun'ichi Nomura <j-nomura@...jp.nec.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 06/94] dm: fix AB-BA deadlock in __dm_destroy()

3.16.7-ckt20 -stable review patch.  If anyone has any objections, please let me know.

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

From: Junichi Nomura <j-nomura@...jp.nec.com>

commit 2a708cff93f1845b9239bc7d6310aef54e716c6a upstream.

__dm_destroy() takes io_barrier SRCU lock (dm_get_live_table) and
suspend_lock in reverse order.  Doing so can cause AB-BA deadlock:

  __dm_destroy                    dm_swap_table
  ---------------------------------------------------
                                  mutex_lock(suspend_lock)
  dm_get_live_table()
    srcu_read_lock(io_barrier)
                                  dm_sync_table()
                                    synchronize_srcu(io_barrier)
                                      .. waiting for dm_put_live_table()
  mutex_lock(suspend_lock)
    .. waiting for suspend_lock

Fix this by taking the locks in proper order.

Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
Fixes: ab7c7bb6f4ab ("dm: hold suspend_lock while suspending device during device deletion")
Acked-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/md/dm.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b3fdf9cfbeb9..91b239489785 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2413,7 +2413,6 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
 	might_sleep();
 
 	spin_lock(&_minor_lock);
-	map = dm_get_live_table(md, &srcu_idx);
 	idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md))));
 	set_bit(DMF_FREEING, &md->flags);
 	spin_unlock(&_minor_lock);
@@ -2423,14 +2422,14 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
 	 * do not race with internal suspend.
 	 */
 	mutex_lock(&md->suspend_lock);
+	map = dm_get_live_table(md, &srcu_idx);
 	if (!dm_suspended_md(md)) {
 		dm_table_presuspend_targets(map);
 		dm_table_postsuspend_targets(map);
 	}
-	mutex_unlock(&md->suspend_lock);
-
 	/* dm_put_live_table must be before msleep, otherwise deadlock is possible */
 	dm_put_live_table(md, srcu_idx);
+	mutex_unlock(&md->suspend_lock);
 
 	/*
 	 * Rare, but there may be I/O requests still going to complete,
--
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