linux-kernel - Re: [PATCH v2] md/raid5: don't allow concurrent reshape with recovery

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Message-ID: <b9fd7105-eadc-29cb-fa2e-24109f4a99b7@linux.dev>
Date:   Wed, 31 May 2023 09:06:47 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Yu Kuai <yukuai1@...weicloud.com>, song@...nel.org,
        pmenzel@...gen.mpg.de
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v2] md/raid5: don't allow concurrent reshape with recovery



On 5/29/23 21:34, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
>
> Commit 0aecb06e2249 ("md/raid5: don't allow replacement while reshape
> is in progress") fixes that replacement can be set if reshape is
> interrupted, which will cause that array can't be assembled.
>
> There is a similar problem on the other side, if recovery is
> interrupted, then reshape can start, which will cause the same problem.
>
> Fix the problem by not starting to reshape while recovery is still in
> progress.
>
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> Changes in v2:
>   - fix some typo in commit message.
>
>   drivers/md/raid5.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 8686d629e3f2..6615abf54d3f 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -8525,6 +8525,7 @@ static int raid5_start_reshape(struct mddev *mddev)
>   	struct r5conf *conf = mddev->private;
>   	struct md_rdev *rdev;
>   	int spares = 0;
> +	int i;
>   	unsigned long flags;
>   
>   	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
> @@ -8536,6 +8537,13 @@ static int raid5_start_reshape(struct mddev *mddev)
>   	if (has_failed(conf))
>   		return -EINVAL;
>   
> +	/* raid5 can't handle concurrent reshape and recovery */
> +	if (mddev->recovery_cp < MaxSector)
> +		return -EBUSY;
> +	for (i = 0; i < conf->raid_disks; i++)
> +		if (rdev_mdlock_deref(mddev, conf->disks[i].replacement))
> +			return -EBUSY;
> +

Does it mean reshape and recovery  can happen in parallel without the 
change?
I really doubt about it given any kind of internal io (resync, reshape 
and recovery)
is handled by resync thread. And IIUC either md_do_sync or md_check_recovery
should avoid it, no need to do it in personality layer.

Thanks,
Guoqing