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

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Message-ID: <CAPhsuW7seCUnt3zt6A_fjTS2diB7qiTE+SZkM6Vh=G26hdwGtg@mail.gmail.com>
Date:   Mon, 13 Jul 2020 23:17:28 -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 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,
Song

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