md: avoid possible spinning md thread at shutdown.

If an md array with externally managed metadata (e.g. DDF or IMSM)
is in use, then we should not set safemode==2 at shutdown because:

1/ this is ineffective: user-space need to be involved in any 'safemode' handling,
2/ The safemode management code doesn't cope with safemode==2 on external metadata
   and md_check_recover enters an infinite loop.

Even at shutdown, an infinite-looping process can be problematic, so this
could cause shutdown to hang.

Cc: stable@vger.kernel.org (any kernel)
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8fda38d23e38..237b7e0ddc7a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8516,7 +8516,8 @@ static int md_notify_reboot(struct notifier_block *this,
                 if (mddev_trylock(mddev)) {
                         if (mddev->pers)
                                 __md_stop_writes(mddev);
-                        mddev->safemode = 2;
+                        if (mddev->persistent)
+                                mddev->safemode = 2;
                         mddev_unlock(mddev);
                 }
                 need_delay = 1;