linux-kernel - Re: [dm-devel] [PATCH -next v2 4/6] md: refactor idle/frozen_sync

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 14 Jun 2023 15:12:01 +0800
From:   Xiao Ni <xni@...hat.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     guoqing.jiang@...ux.dev, agk@...hat.com, snitzer@...nel.org,
        dm-devel@...hat.com, song@...nel.org, linux-raid@...r.kernel.org,
        yangerkun@...wei.com, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [dm-devel] [PATCH -next v2 4/6] md: refactor idle/frozen_sync_thread()
 to fix deadlock

On Wed, Jun 14, 2023 at 10:04 AM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2023/06/14 9:48, Yu Kuai 写道:
>
>
> >>
> >> In the patch, sync_seq is added in md_reap_sync_thread. In
> >> idle_sync_thread, if sync_seq isn't equal
> >>
> >> mddev->sync_seq, it should mean there is someone that stops the sync
> >> thread already, right? Why do
> >>
> >> you say 'new started sync thread' here?
>
> If someone stops the sync thread, and new sync thread is not started,
> then this sync_seq won't make a difference, above wait_event() will not
> wait because !test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) will pass.
> So 'sync_seq' is only used when the old sync thread stops and new sync
> thread starts, add 'sync_seq' will bypass this case.

Hi

If a new sync thread starts, why can sync_seq be different? sync_seq
is only added in md_reap_sync_thread. And when a new sync request
starts, it can't stop the sync request again?

Af first, the sync_seq is 0

admin1
echo idle > sync_action
idle_sync_thread(sync_seq is 1)
echo resync > sync_action (new sync)

Then admin2 echos idle > sync_action, sync_seq is still 1

Regards
Xiao

>
> Thanks,
> Kuai
>