linux-kernel - Re: [dm-devel] [PATCH -next v2 3/6] md: add a mutex to synchronize idle and frozen in action

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Message-ID: <CAPhsuW5nyv0=e3WR+B4gQmHo9O0cDBmzpEOZwXTLbvPzjX5iDw@mail.gmail.com>
Date:   Thu, 15 Jun 2023 23:41:42 -0700
From:   Song Liu <song@...nel.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     Xiao Ni <xni@...hat.com>, guoqing.jiang@...ux.dev, agk@...hat.com,
        snitzer@...nel.org, dm-devel@...hat.com, yi.zhang@...wei.com,
        yangerkun@...wei.com, linux-kernel@...r.kernel.org,
        linux-raid@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [dm-devel] [PATCH -next v2 3/6] md: add a mutex to synchronize
 idle and frozen in action_store()

On Tue, Jun 13, 2023 at 6:15 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> 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@...wei.com>
> >>
> >> 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@...wei.com>
> >> ---
> >>   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.

I fixed this one and applied the set to md-next.

Thanks,
Song