[dm-devel] Patch "dm: don't lock fs when the map is NULL during suspend or resume" has been added to the 5.15-stable tree

[Sasha Levin]

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

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

to the 5.15-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-don-t-lock-fs-when-the-map-is-null-during-suspend.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.



commit aae8e4e2c44e6fbcbc3437c79cd13b567bc51bf7
Author: Li Lingfeng <lilingfeng3 at huawei.com>
Date:   Thu Jun 1 14:14:23 2023 +0800

    dm: don't lock fs when the map is NULL during suspend or resume
    
    [ Upstream commit 2760904d895279f87196f0fa9ec570c79fe6a2e4 ]
    
    As described in commit 38d11da522aa ("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 38d11da522aa 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: 38d11da522aa ("dm: don't lock fs when the map is NULL in process of resume")
    Signed-off-by: Li Lingfeng <lilingfeng3 at huawei.com>
    Signed-off-by: Mike Snitzer <snitzer at kernel.org>
    Signed-off-by: Sasha Levin <sashal at kernel.org>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 438c0b77bb48c..815c41e1ebdb8 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1145,13 +1145,10 @@ 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))
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8bc121d394471..d6285a23dc3ed 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2526,6 +2526,10 @@ int dm_suspend(struct mapped_device *md, unsigned 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)