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

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Date:   Mon, 5 Jun 2023 16:59:29 -0700
From:   Song Liu <song@...nel.org>
To:     Guoqing Jiang <guoqing.jiang@...ux.dev>
Cc:     Yu Kuai <yukuai1@...weicloud.com>, pmenzel@...gen.mpg.de,
        linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2] md/raid5: don't allow concurrent reshape with recovery

On Wed, May 31, 2023 at 12:34 AM Guoqing Jiang <guoqing.jiang@...ux.dev> wrote:
>
>
>
> On 5/31/23 11:20, Yu Kuai wrote:
> > Hi,
> >
> > 在 2023/05/31 9:49, Guoqing Jiang 写道:
> >>
> >>
> >> On 5/31/23 09:22, Yu Kuai wrote:
> >>> Hi,
> >>>
> >>> 在 2023/05/31 9:06, Guoqing Jiang 写道:
> >>>>
> >>>>
> >>>> 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.
> >>
> >> I just pulled md tree, but can't find the commit id either in md-next
> >> or md-fixes .
> >> gjiang@pc:~/storage/md> git branch
> >>   master
> >>   md-fixes
> >> * md-next
> >> gjiang@pc:~/storage/md> git branch --contain 0aecb06e2249
> >> error: malformed object name 0aecb06e2249
> >>
> >>>>> 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.
> >>>>
> >>>
> >>> They can't, in this case recovery is interrupted, then recovery can't
> >>> make progress, and md_check_recovery() will start reshape, and after
> >>> reshape is done, recovery will continue, and data will be corrupted
> >>> because raid456 reshape doesn't handle replacement.
> >>
> >> So, do reshape first then recovery, right? I don't see concurrent
> >> reshape and recovery
> >> happen based on your description, if concurrent reshape and recovery
> >> is possible
> >> then I believe we really have big trouble.
> >
> > Yes, reshape first, and yes they can't concurrent.
>
> Then the subject, commit message and above comment are confusing given
> they can't happen
> even without your change.
>

I updated the commit message as:

    md/raid5: don't start reshape when recovery or replace is in progress

    When recovery is interrupted (reboot, etc.) check for MD_RECOVERY_RUNNING
    is not enough to tell recovery is in progress. Also check recovery_cp
   before starting reshape.

Please let me know if this doesn't make sense.

Thanks,
Song