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

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

On 6/23/22 7:32 AM, Song Liu wrote:
> On Mon, Jun 20, 2022 at 8:11 PM Guoqing Jiang <guoqing.jiang@linux.dev> wrote:
>> 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.
>> +                                */
> Hmm.. do we really need to handle reshape_position changed case? What would
> break if we don't?

I want to make the behavior consistent with previous code, and 
reshape_position_store
can change it as said in comment.

Anyway, I didn't see regression with mdadm test with or without setting 
reshape_position,
so it is a more conservative way to avoid potential issue. I will remove 
it if you think it is
not necessary.

Thanks,
Guoqing