[PATCH V2] md: unlock mddev before reap sync_thread in action_store

[Guoqing Jiang <guoqing.jiang@linux.dev>]

Since the bug which commit 8b48ec23cc51a ("md: don't unregister sync_thread
with reconfig_mutex held") fixed is related with action_store path, other
callers which reap sync_thread didn't need to be changed.

Let's pull md_unregister_thread from md_reap_sync_thread, then fix previous
bug with belows.

1. unlock mddev before md_reap_sync_thread in action_store.
2. save reshape_position before unlock, then restore it to ensure position
   not changed accidentally by others.

Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
---
V2 changes:
1. add set_bit(MD_RECOVERY_INTR, &mddev->recovery) before unregister sync thread

And I didn't find regression with this version after run mdadm tests.

 drivers/md/dm-raid.c |  1 +
 drivers/md/md.c      | 19 +++++++++++++++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 9526ccbedafb..d43b8075c055 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3725,6 +3725,7 @@ 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_unregister_thread(&mddev->sync_thread);
 			md_reap_sync_thread(mddev);
 		}
 	} else if (decipher_sync_action(mddev, mddev->recovery) != st_idle)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index c7ecb0bffda0..04bab0511312 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4830,6 +4830,19 @@ action_store(struct mddev *mddev, const char *page, size_t len)
 			if (work_pending(&mddev->del_work))
 				flush_workqueue(md_misc_wq);
 			if (mddev->sync_thread) {
+				sector_t save_rp = mddev->reshape_position;
+
+				mddev_unlock(mddev);
+				set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+				md_unregister_thread(&mddev->sync_thread);
+				mddev_lock_nointr(mddev);
+				/*
+				 * set RECOVERY_INTR again and restore reshape
+				 * position in case others changed them after
+				 * got lock, eg, reshape_position_store and
+				 * md_check_recovery.
+				 */
+				mddev->reshape_position = save_rp;
 				set_bit(MD_RECOVERY_INTR, &mddev->recovery);
 				md_reap_sync_thread(mddev);
 			}
@@ -6197,6 +6210,7 @@ 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_unregister_thread(&mddev->sync_thread);
 		md_reap_sync_thread(mddev);
 	}
 
@@ -9303,6 +9317,7 @@ void md_check_recovery(struct mddev *mddev)
 			 * ->spare_active and clear saved_raid_disk
 			 */
 			set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+			md_unregister_thread(&mddev->sync_thread);
 			md_reap_sync_thread(mddev);
 			clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
 			clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
@@ -9338,6 +9353,7 @@ void md_check_recovery(struct mddev *mddev)
 			goto unlock;
 		}
 		if (mddev->sync_thread) {
+			md_unregister_thread(&mddev->sync_thread);
 			md_reap_sync_thread(mddev);
 			goto unlock;
 		}
@@ -9417,8 +9433,7 @@ void md_reap_sync_thread(struct mddev *mddev)
 	sector_t old_dev_sectors = mddev->dev_sectors;
 	bool is_reshaped = false;
 
-	/* resync has finished, collect result */
-	md_unregister_thread(&mddev->sync_thread);
+	/* sync_thread should be unregistered, collect result */
 	if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&
 	    !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
 	    mddev->degraded != mddev->raid_disks) {
-- 
2.31.1