dm: fix AB-BA deadlock in __dm_destroy()

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@ce.jp.nec.com>
Fixes: ab7c7bb6f4ab ("dm: hold suspend_lock while suspending device during device deletion")
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b3fdf9cfbeb94c949f5cf6b5dc999ec51acac2ac..91b2394897857ecfd402863f837b4643ccc808ab 100644 (file)
--- 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,