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Subject: Re: [PATCH -next 1/2] md: don't quiesce in mddev_suspend()
To:     Yu Kuai <yukuai1@huaweicloud.com>, xni@redhat.com, song@kernel.org,
        colyli@suse.de
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230628012931.88911-1-yukuai1@huaweicloud.com>
 <20230628012931.88911-2-yukuai1@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <10137916-9feb-8ab6-e157-8c66bbad1932@huaweicloud.com>
Date:   Wed, 28 Jun 2023 14:29:29 +0800
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Hi,

?? 2023/06/28 9:29, Yu Kuai д??:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Some levels doesn't implement "pers->quiesce", for example
> raid0_quiesce() is empty, and now that all levels will drop 'active_io'
> until io is done, wait for 'active_io' to be 0 is enough to make sure all
> normal io is done, and percpu_ref_kill() for 'active_io' will make sure
> no new normal io can be dispatched. There is no need to call
> "pers->quiesce" anymore from mddev_suspend().

Just found that this patch actually prevent null_ptr_deref in some cases
that "pers->quiesce" is NULl for some personalities, and caller of
mddev_suspend() doesn't check this. For example, suspend_lo_store()
checks "pers->quiesce" is not NULL before calling mddev_suspend(), while
suspend_hi_store() doesn't.

Thanks,
Kuai
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>   drivers/md/md.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index abb616720393..962dacfd98cf 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -453,7 +453,6 @@ void mddev_suspend(struct mddev *mddev)
>   		mddev->pers->prepare_suspend(mddev);
>   
>   	wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
> -	mddev->pers->quiesce(mddev, 1);
>   	clear_bit_unlock(MD_ALLOW_SB_UPDATE, &mddev->flags);
>   	wait_event(mddev->sb_wait, !test_bit(MD_UPDATING_SB, &mddev->flags));
>   
> @@ -472,7 +471,6 @@ void mddev_resume(struct mddev *mddev)
>   		return;
>   	percpu_ref_resurrect(&mddev->active_io);
>   	wake_up(&mddev->sb_wait);
> -	mddev->pers->quiesce(mddev, 0);
>   
>   	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
>   	md_wakeup_thread(mddev->thread);
>