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

[Song Liu <song@kernel.org>]

On Wed, Jun 22, 2022 at 6:30 PM Guoqing Jiang <guoqing.jiang@linux.dev> wrote:
>
>
>
> 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.

I see. I will apply the patch as-is.

Thanks,
Song

>
> 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.