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

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Date:   Mon, 13 Jul 2020 23:41:12 -0700
From:   Junxiao Bi <junxiao.bi@...cle.com>
To:     Song Liu <song@...nel.org>
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 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.

Thanks,

Junxiao.

>
> Thanks,
> Song
>
> [...]