On Tue, 2 Sep 2014 15:07:26 -0700 Eivind Sarto <eivindsarto@xxxxxxxxx> wrote:
>
> On Sep 2, 2014, at 12:24 PM, Brassow Jonathan <jbrassow@xxxxxxxxxx> wrote:
>
> >
> > On Aug 29, 2014, at 2:29 PM, Eivind Sarto wrote:
> >
> >> I am seeing occasional data corruption during raid1 resync.
> >> Reviewing the raid1 code, I suspect that commit 79ef3a8aa1cb1523cc231c9a90a278333c21f761 introduced a bug.
> >> Prior to this commit raise_barrier() used to wait for conf->nr_pending to become zero. It no longer does this.
> >> It is not easy to reproduce the corruption, so I wanted to ask about the following potential fix while I am still testing it.
> >> Once I validate that the fix indeed works, I will post a proper patch.
> >> Do you have any feedback?
> >>
> >> — drivers/md/raid1.c 2014-08-22 15:19:15.000000000 -0700
> >> +++ /tmp/raid1.c 2014-08-29 12:07:51.000000000 -0700
> >> @@ -851,7 +851,7 @@ static void raise_barrier(struct r1conf
> >> * handling.
> >> */
> >> wait_event_lock_irq(conf->wait_barrier,
> >> - !conf->array_frozen &&
> >> + !conf->array_frozen && !conf->nr_pending &&
> >> conf->barrier < RESYNC_DEPTH &&
> >> (conf->start_next_window >=
> >> conf->next_resync + RESYNC_SECTORS),
> >
> > This patch does not work - at least, it doesn't fix the issues I'm seeing. My system hangs (in various places, like the resync thread) after commit 79ef3a8. When testing this patch, I also added some code to dm-raid.c to allow me to print-out some of the variables when I encounter a problem. After applying this patch and printing the variables, I see:
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: start_next_window = 12288
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: current_window_requests = -46
> > 5257
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: next_window_requests = -11562
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: nr_pending = 0
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: nr_waiting = 0
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: nr_queued = 0
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: barrier = 1
> > Sep 2 14:04:15 bp-01 kernel: device-mapper: raid: array_frozen = 0
> >
> > Some of those values look pretty bizarre to me and suggest the accounting is pretty messed up.
> >
> > brassow
> >
>
> After reviewing commit 79ef3a8aa1cb1523cc231c9a90a278333c21f761 I notice that wait_barrier() will now only exclude writes. User reads are not excluded even if the fall within the resync window.
> The old implementation used to exclude both reads and writes while resync-IO is active.
> Could this be a cause of data corruption?
>
Could be.
From read_balance:
if (conf->mddev->recovery_cp < MaxSector &&
(this_sector + sectors >= conf->next_resync))
choose_first = 1;
else
choose_first = 0;
This used to be safe because a read immediately before next_resync would wait
until all resync requests completed. But now that read requests don't block
it isn't safe.
Probably best to make this:
choose_first = (conf->mddev->recovery_cp < this_sector + sectors);
Can you test that?
Thanks,
NeilBrown
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