[PATCH AUTOSEL 4.19 18/27] md: don't unregister sync_thread with reconfig_mutex held

[Sasha Levin <sashal@kernel.org>]

From: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>

[ Upstream commit 8b48ec23cc51a4e7c8dbaef5f34ebe67e1a80934 ]

Unregister sync_thread doesn't need to hold reconfig_mutex since it
doesn't reconfigure array.

And it could cause deadlock problem for raid5 as follows:

1. process A tried to reap sync thread with reconfig_mutex held after echo
   idle to sync_action.
2. raid5 sync thread was blocked if there were too many active stripes.
3. SB_CHANGE_PENDING was set (because of write IO comes from upper layer)
   which causes the number of active stripes can't be decreased.
4. SB_CHANGE_PENDING can't be cleared since md_check_recovery was not able
   to hold reconfig_mutex.

More details in the link:
https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@molgen.mpg.de/T/#t

And add one parameter to md_reap_sync_thread since it could be called by
dm-raid which doesn't hold reconfig_mutex.

Reported-and-tested-by: Donald Buczek <buczek@molgen.mpg.de>
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/dm-raid.c |  2 +-
 drivers/md/md.c      | 14 +++++++++-----
 drivers/md/md.h      |  2 +-
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index b16332917220..0be03123d6a2 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3710,7 +3710,7 @@ static int raid_message(struct dm_target *ti, unsigned int argc, char **argv,
 	if (!strcasecmp(argv[0], "idle") || !strcasecmp(argv[0], "frozen")) {
 		if (mddev->sync_thread) {
 			set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-			md_reap_sync_thread(mddev);
+			md_reap_sync_thread(mddev, false);
 		}
 	} else if (decipher_sync_action(mddev, mddev->recovery) != st_idle)
 		return -EBUSY;
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 7e0477e883c7..da7954eff4d7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4611,7 +4611,7 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			flush_workqueue(md_misc_wq);
 			if (mddev->sync_thread) {
 				set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-				md_reap_sync_thread(mddev);
+				md_reap_sync_thread(mddev, true);
 			}
 			mddev_unlock(mddev);
 		}
@@ -5871,7 +5871,7 @@ static void __md_stop_writes(struct mddev *mddev)
 	flush_workqueue(md_misc_wq);
 	if (mddev->sync_thread) {
 		set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-		md_reap_sync_thread(mddev);
+		md_reap_sync_thread(mddev, true);
 	}
 
 	del_timer_sync(&mddev->safemode_timer);
@@ -8893,7 +8893,7 @@ void md_check_recovery(struct mddev *mddev)
 			 * ->spare_active and clear saved_raid_disk
 			 */
 			set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-			md_reap_sync_thread(mddev);
+			md_reap_sync_thread(mddev, true);
 			clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
 			clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 			clear_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags);
@@ -8928,7 +8928,7 @@ void md_check_recovery(struct mddev *mddev)
 			goto unlock;
 		}
 		if (mddev->sync_thread) {
-			md_reap_sync_thread(mddev);
+			md_reap_sync_thread(mddev, true);
 			goto unlock;
 		}
 		/* Set RUNNING before clearing NEEDED to avoid
@@ -9001,12 +9001,16 @@ void md_check_recovery(struct mddev *mddev)
 }
 EXPORT_SYMBOL(md_check_recovery);
 
-void md_reap_sync_thread(struct mddev *mddev)
+void md_reap_sync_thread(struct mddev *mddev, bool reconfig_mutex_held)
 {
 	struct md_rdev *rdev;
 
+	if (reconfig_mutex_held)
+		mddev_unlock(mddev);
 	/* resync has finished, collect result */
 	md_unregister_thread(&mddev->sync_thread);
+	if (reconfig_mutex_held)
+		mddev_lock_nointr(mddev);
 	if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&
 	    !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
 	    mddev->degraded != mddev->raid_disks) {
diff --git a/drivers/md/md.h b/drivers/md/md.h
index cce62bbc2bcb..027b220dec14 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -674,7 +674,7 @@ extern struct md_thread *md_register_thread(
 extern void md_unregister_thread(struct md_thread **threadp);
 extern void md_wakeup_thread(struct md_thread *thread);
 extern void md_check_recovery(struct mddev *mddev);
-extern void md_reap_sync_thread(struct mddev *mddev);
+extern void md_reap_sync_thread(struct mddev *mddev, bool reconfig_mutex_held);
 extern int mddev_init_writes_pending(struct mddev *mddev);
 extern bool md_write_start(struct mddev *mddev, struct bio *bi);
 extern void md_write_inc(struct mddev *mddev, struct bio *bi);
-- 
2.35.1