Hi,

在 2024/02/18 13:56, Xiao Ni 写道:

On Thu, Feb 1, 2024 at 5:30 PM Yu Kuai [off-list ref] wrote:

quoted

From: Yu Kuai <redacted>

stop_sync_thread() will interrupt md_do_sync(), and md_do_sync() must
set MD_RECOVERY_DONE, so that follow up md_check_recovery() will
unregister sync_thread, clear MD_RECOVERY_RUNNING and wake up
stop_sync_thread().

If MD_RECOVERY_WAIT is set or the array is read-only, md_do_sync() will
return without setting MD_RECOVERY_DONE, and after commit f52f5c71f3d4
("md: fix stopping sync thread"), dm-raid switch from
md_reap_sync_thread() to stop_sync_thread() to unregister sync_thread
from md_stop() and md_stop_writes(), causing the test
shell/lvconvert-raid-reshape.sh hang.

We shouldn't switch back to md_reap_sync_thread() because it's
problematic in the first place. Fix the problem by making sure
md_do_sync() will set MD_RECOVERY_DONE.

Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Closes: https://lore.kernel.org/all/ece2b06f-d647-6613-a534-ff4c9bec1142@redhat.com/ (local)
Fixes: d5d885fd514f ("md: introduce new personality funciton start()")
Fixes: 5fd6c1dce06e ("[PATCH] md: allow checkpoint of recovery with version-1 superblock")
Fixes: f52f5c71f3d4 ("md: fix stopping sync thread")
Signed-off-by: Yu Kuai <redacted>
---
  drivers/md/md.c | 12 ++++++++----
  1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6906d023f1d6..c65dfd156090 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -8788,12 +8788,16 @@ void md_do_sync(struct md_thread *thread)
         int ret;

         /* just incase thread restarts... */
-       if (test_bit(MD_RECOVERY_DONE, &mddev->recovery) ||
-           test_bit(MD_RECOVERY_WAIT, &mddev->recovery))
+       if (test_bit(MD_RECOVERY_DONE, &mddev->recovery))
                 return;
-       if (!md_is_rdwr(mddev)) {/* never try to sync a read-only array */
+
+       if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
+               goto skip;
+
+       if (test_bit(MD_RECOVERY_WAIT, &mddev->recovery) ||
+           !md_is_rdwr(mddev)) {/* never try to sync a read-only array */
                 set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-               return;
+               goto skip;
         }

Hi all

I have a question here. The codes above means if MD_RECOVERY_WAIT is
set, it sets MD_RECOVERY_INTR. If so, the sync thread can't happen.
But from the codes in md_start function:

                 set_bit(MD_RECOVERY_WAIT, &mddev->recovery);
                 md_wakeup_thread(mddev->thread);
                 ret = mddev->pers->start(mddev);
                 clear_bit(MD_RECOVERY_WAIT, &mddev->recovery);
                 md_wakeup_thread(mddev->sync_thread);

MD_RECOVERY_WAIT means "it'll run sync thread later not interrupt it".
I guess this patch can introduce a new bug for raid5 journal?

I'm not sure what kind of problem you're talking about. After patch 4,
md_start_sync() should be the only place to register sync_thread, hence
md_start() should not see registered sync_thread. Perhaps
MD_RECOVERY_WAIT and md_wakeup_thread(mddev->sync_thread) can be removed
after patch 4?

You must make sure md_do_sync() is called after this if sync_thread is 
already registered, and I don't understand yet how this is guranteed. :(

Thanks,
Kuai

Regards
Xiao

quoted

         if (mddev_is_clustered(mddev)) {
--
2.39.2

.