[PATCH 3.12 1/5] dm: fix AB-BA deadlock in __dm_destroy()

[Jiri Slaby]

From: Junichi Nomura <j-nomura@xxxxxxxxxxxxx>

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

===============

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@xxxxxxxxxxxxx>
Fixes: ab7c7bb6f4ab ("dm: hold suspend_lock while suspending device during device deletion")
Acked-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 drivers/md/dm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 5a0b1742f794..de444d3ae293 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2444,14 +2444,14 @@ 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,
-- 
2.10.1