[PATCH] md: fix stop_sync_thread() hang on new sync in idle path

[PATCH] md: fix stop_sync_thread() hang on new sync in idle path

[Li Youhong]

From: Li Youhong <liyouhong@kylinos.cn>

stop_sync_thread() waits for either MD_RECOVERY_RUNNING to be cleared,
or (when MD_RECOVERY_FROZEN is clear) for mddev->sync_seq to change.
The sync_seq counter is only incremented when a sync thread is reaped
in md_reap_sync_thread(), not on the md_start_sync() not_running path.

If the previous sync attempt took the not_running path, sync_seq does
not advance. If mddev->thread then queues and runs a new sync in the
window between flush_work() and wait_event(), that new sync may start
a real sync thread, leaving MD_RECOVERY_RUNNING set while sync_seq is
still unchanged. md_idle_sync_thread() then waits until that new sync
thread is reaped and sync_seq finally changes, even though it only
needs to wait for the current sync attempt to finish.

Fix this by incrementing sync_seq on the not_running path as well, so
that the wait condition correctly observes the current sync attempt has
completed.

Fixes: a17d1bca5aba ("md: fix stopping sync thread")
Cc: stable@vger.kernel.org
Signed-off-by: Li Youhong <liyouhong@kylinos.cn>
---
 drivers/md/md.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 68a72513e884..1970c945e597 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -10352,6 +10352,7 @@ static void md_start_sync(struct work_struct *ws)
 	clear_bit(MD_RECOVERY_REQUESTED, &mddev->recovery);
 	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
 	clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+	atomic_inc(&mddev->sync_seq);
 	mddev_unlock(mddev);
 	/*
 	 * md_start_sync was triggered by MD_RECOVERY_NEEDED, so we should

Re: [PATCH] md: fix stop_sync_thread() hang on new sync in idle path

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] md: Fixes trailer references stable backport SHA instead of
  mainline SHA
--

commit 5befe56f6aae61b7aa7d4c1baac50a35a4c54849
Author: Li Youhong <liyouhong@kylinos.cn>

> md: fix stop_sync_thread() hang on new sync in idle path
>
> stop_sync_thread() waits for either MD_RECOVERY_RUNNING to be cleared,
> or (when MD_RECOVERY_FROZEN is clear) for mddev->sync_seq to change.
> The sync_seq counter is only incremented when a sync thread is reaped
> in md_reap_sync_thread(), not on the md_start_sync() not_running path.
>
> If the previous sync attempt took the not_running path, sync_seq does
> not advance. If mddev->thread then queues and runs a new sync in the
> window between flush_work() and wait_event(), that new sync may start
> a real sync thread, leaving MD_RECOVERY_RUNNING set while sync_seq is
> still unchanged. md_idle_sync_thread() then waits until that new sync
> thread is reaped and sync_seq finally changes, even though it only
> needs to wait for the current sync attempt to finish.
>
> Fix this by incrementing sync_seq on the not_running path as well, so
> that the wait condition correctly observes the current sync attempt has
> completed.
>
> Fixes: a17d1bca5aba ("md: fix stopping sync thread")
> Cc: stable@vger.kernel.org
> Signed-off-by: Li Youhong <liyouhong@kylinos.cn>

[Severity: Low]
a17d1bca5aba ("md: fix stopping sync thread") is a stable-tree backport
rather than the mainline commit in the branch history.  Should the Fixes:
tag reference the upstream commit instead:

  Fixes: f52f5c71f3d4 ("md: fix stopping sync thread")

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261112092634.1700963-1-dayou5941@163.com?part=1