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

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Date:   Wed, 14 Jun 2023 10:04:33 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Yu Kuai <yukuai1@...weicloud.com>, Xiao Ni <xni@...hat.com>,
        guoqing.jiang@...ux.dev, agk@...hat.com, snitzer@...nel.org,
        dm-devel@...hat.com, song@...nel.org
Cc:     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

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.

Thanks,
Kuai