linux-kernel - Re: [PATCH] md: fix deadlock causing by sysfs

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Message-ID: <CAPhsuW4GQK7hS4AOpJJ1mEE8gbFgo+n+XCQ2fvW94QnZhA6ivQ@mail.gmail.com>
Date:   Tue, 14 Jul 2020 09:18:39 -0700
From:   Song Liu <song@...nel.org>
To:     Junxiao Bi <junxiao.bi@...cle.com>
Cc:     linux-raid <linux-raid@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] md: fix deadlock causing by sysfs_notify

On Mon, Jul 13, 2020 at 11:41 PM Junxiao Bi <junxiao.bi@...cle.com> wrote:
>
> On 7/13/20 11:17 PM, Song Liu wrote:
>
> > On Thu, Jul 9, 2020 at 4:36 PM Junxiao Bi <junxiao.bi@...cle.com> wrote:
> >> The following deadlock was captured. The first process is holding 'kernfs_mutex'
> >> and hung by io. The io was staging in 'r1conf.pending_bio_list' of raid1 device,
> >> this pending bio list would be flushed by second process 'md127_raid1', but
> >> it was hung by 'kernfs_mutex'. Using sysfs_notify_dirent_safe() to replace
> >> sysfs_notify() can fix it. There were other sysfs_notify() invoked from io
> >> path, removed all of them.
> >>
> > [...]
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Junxiao Bi <junxiao.bi@...cle.com>
> > Thanks for the patch. It looks good in general. One question though, do we
> > need the same change the following line in md.c:level_store()?
> >
> >      sysfs_notify(&mddev->kobj, NULL, "level");
>
> Thanks for the review. This one is not in io path, looks it's safe. I
> can change it if you want to align it with others.

This one is the only leftover. Let's also change it.

Thanks,
Song