linux-kernel - Re: [PATCH v5 04/14] md: don't register sync

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Date: Wed, 28 Feb 2024 20:57:16 +0800
From: Xiao Ni <xni@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: mpatocka@...hat.com, heinzm@...hat.com, blazej.kucman@...ux.intel.com, 
	agk@...hat.com, snitzer@...nel.org, dm-devel@...ts.linux.dev, song@...nel.org, 
	neilb@...e.de, shli@...com, akpm@...l.org, linux-kernel@...r.kernel.org, 
	linux-raid@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com, 
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v5 04/14] md: don't register sync_thread for reshape directly

On Wed, Feb 28, 2024 at 8:44 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2024/02/28 20:07, Xiao Ni 写道:
> > I have a question here. Is it the reason sync_thread can't run
> > md_do_sync because kthread_should_stop, so it doesn't have the chance to
> > set MD_RECOVERY_DONE? Why creating sync thread in md_check_recovery
> > doesn't have this problem? Could you explain more about this?
>
> raid10_run() only register sync_thread, without calling
> md_wakeup_thread() to set the bit 'THREAD_WAKEUP', md_do_sync() will not
> be executed.

I c. The user is responsible to wake up the thread. If raid10 wakes up
the thread in the right way, we don't need to move register reshape
thread to md_check_recovery, right?

>
> raid5 defines 'pers->start' hence md_start() will call
> md_wakeup_thread().
>
> md_start_sync() will always call md_wakeup_thread() hence there is no
> such problem.
>
> BTW, this patch fix the same problem as you mentioned in your other
> thread:
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 2266358d8074..54790261254d 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -4904,6 +4904,7 @@ static void stop_sync_thread(struct mddev *mddev,
> bool locked, bool check_seq)
>          * never happen
>          */
>         md_wakeup_thread_directly(mddev->sync_thread);
> +       md_wakeup_thread(mddev->sync_thread);
>         if (work_pending(&mddev->sync_work))
>                 flush_work(&mddev->sync_work);

The first patch of my patch set has this already. Maybe it's the
reason that my patch01 can fix this similar problem.

>
> However, I think the one to register sync_thread is responsible to wake
> it up.

Agree, the user that registers thread should wake it up. So start/stop
sync thread apis are common. And they can be called by many users.

Best Regards
Xiao
>
> Thanks,
> Kuai
>