Re: [dm-devel] [PATCH -next v2 4/6] md: refactor idle/frozen_sync_thread() to fix deadlock

[Xiao Ni]

On Wed, Jun 14, 2023 at 10:04 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> 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
>