Patch "dm: fix AB-BA deadlock in __dm_destroy()" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

dm: fix AB-BA deadlock in __dm_destroy()

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-fix-ab-ba-deadlock-in-__dm_destroy.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Junichi Nomura <[email protected]>
Date: Thu, 1 Oct 2015 08:31:51 +0000
Subject: dm: fix AB-BA deadlock in __dm_destroy()

From: Junichi Nomura <[email protected]>

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.

---
 drivers/md/dm.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

@@ -2925,8 +2925,6 @@ static void __dm_destroy(struct mapped_d
 
 	might_sleep();
 
-	map = dm_get_live_table(md, &srcu_idx);
-
 	spin_lock(&_minor_lock);
 	idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md))));
 	set_bit(DMF_FREEING, &md->flags);

@@ -2940,14 +2938,14 @@ static void __dm_destroy(struct mapped_d
 	 * 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,

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/dm-fix-ab-ba-deadlock-in-__dm_destroy.patch