Re: [dm-devel] [PATCH -next v2 3/6] md: add a mutex to synchronize idle and frozen in action_store()

[Yu Kuai]

Hi,

在 2023/06/13 22:43, Xiao Ni 写道:
> 在 2023/5/29 下午9:20, Yu Kuai 写道:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > Currently, for idle and frozen, action_store will hold 'reconfig_mutex'
> > and call md_reap_sync_thread() to stop sync thread, however, this will
> > cause deadlock (explained in the next patch). In order to fix the
> > problem, following patch will release 'reconfig_mutex' and wait on
> > 'resync_wait', like md_set_readonly() and do_md_stop() does.
> >
> > Consider that action_store() will set/clear 'MD_RECOVERY_FROZEN'
> > unconditionally, which might cause unexpected problems, for example,
> > frozen just set 'MD_RECOVERY_FROZEN' and is still in progress, while
> > 'idle' clear 'MD_RECOVERY_FROZEN' and new sync thread is started, which
> > might starve in progress frozen. A mutex is added to synchronize idle
> > and frozen from action_store().
> >
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   drivers/md/md.c | 5 +++++
> >   drivers/md/md.h | 3 +++
> >   2 files changed, 8 insertions(+)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 23e8e7eae062..63a993b52cd7 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -644,6 +644,7 @@ void mddev_init(struct mddev *mddev)
> >       mutex_init(&mddev->open_mutex);
> >       mutex_init(&mddev->reconfig_mutex);
> >       mutex_init(&mddev->delete_mutex);
> > +    mutex_init(&mddev->sync_mutex);
> >       mutex_init(&mddev->bitmap_info.mutex);
> >       INIT_LIST_HEAD(&mddev->disks);
> >       INIT_LIST_HEAD(&mddev->all_mddevs);
> > @@ -4785,14 +4786,18 @@ static void stop_sync_thread(struct mddev *mddev)
> >   static void idle_sync_thread(struct mddev *mddev)
> >   {
> > +    mutex_lock(&mddev->sync_mutex);
> >       clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
> >       stop_sync_thread(mddev);
> > +    mutex_unlock(&mddev->sync_mutex);
> >   }
> >   static void frozen_sync_thread(struct mddev *mddev)
> >   {
> > +    mutex_init(&mddev->delete_mutex);
>
>
> typo error? It should be mutex_lock(&mddev->sync_mutex); ?

Yes, and thanks for spotting this, this looks like I did this while
rebasing.

Thanks,
Kuai
> Regards
>
> Xiao
>
> >       set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
> >       stop_sync_thread(mddev);
> > +    mutex_unlock(&mddev->sync_mutex);
> >   }
> >   static ssize_t
> > diff --git a/drivers/md/md.h b/drivers/md/md.h
> > index bfd2306bc750..2fa903de5bd0 100644
> > --- a/drivers/md/md.h
> > +++ b/drivers/md/md.h
> > @@ -537,6 +537,9 @@ struct mddev {
> >       /* Protect the deleting list */
> >       struct mutex            delete_mutex;
> > +    /* Used to synchronize idle and frozen for action_store() */
> > +    struct mutex            sync_mutex;
> > +
> >       bool    has_superblocks:1;
> >       bool    fail_last_dev:1;
> >       bool    serialize_policy:1;
>
> .