dm: don't lock fs when the map is NULL during suspend or resume

As described in commit 38d11da5 ("dm: don't lock fs when the map is
NULL in process of resume"), a deadlock may be triggered between
do_resume() and do_mount().

This commit preserves the fix from commit 38d11da5 but moves it to
where it also serves to fix a similar deadlock between do_suspend()
and do_mount().  It does so, if the active map is NULL, by clearing
DM_SUSPEND_LOCKFS_FLAG in dm_suspend() which is called by both
do_suspend() and do_resume().

Fixes: 38d11da5 ("dm: don't lock fs when the map is NULL in process of resume")
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-ioctl.c

@@ -1168,13 +1168,10 @@ static int do_resume(struct dm_ioctl *param)
 	/* Do we need to load a new map ? */
 	if (new_map) {
 		sector_t old_size, new_size;
-		int srcu_idx;
 
 		/* Suspend if it isn't already suspended */
-		old_map = dm_get_live_table(md, &srcu_idx);
-		if ((param->flags & DM_SKIP_LOCKFS_FLAG) || !old_map)
+		if (param->flags & DM_SKIP_LOCKFS_FLAG)
 			suspend_flags &= ~DM_SUSPEND_LOCKFS_FLAG;
-		dm_put_live_table(md, srcu_idx);
 		if (param->flags & DM_NOFLUSH_FLAG)
 			suspend_flags |= DM_SUSPEND_NOFLUSH_FLAG;
 		if (!dm_suspended_md(md))

drivers/md/dm.c

@@ -2808,6 +2808,10 @@ int dm_suspend(struct mapped_device *md, unsigned int suspend_flags)
 	}
 
 	map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
+	if (!map) {
+		/* avoid deadlock with fs/namespace.c:do_mount() */
+		suspend_flags &= ~DM_SUSPEND_LOCKFS_FLAG;
+	}
 
 	r = __dm_suspend(md, map, suspend_flags, TASK_INTERRUPTIBLE, DMF_SUSPENDED);
 	if (r)