From: Dominik Brodowski <linux@dominikbrodowski.net>
To: NeilBrown <neilb@suse.com>
Cc: Shaohua Li <shli@fb.com>, David R <david@unsolicited.net>,
linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
tj@kernel.org
Subject: Re: [MD] Crash with 4.12+ kernel and high disk load -- bisected to 4ad23a976413: MD: use per-cpu counter for writes_pending
Date: Tue, 8 Aug 2017 11:06:01 +0200 [thread overview]
Message-ID: <20170808090600.GA28583@isilmar-4.linta.de> (raw)
In-Reply-To: <20170808073614.GA21316@light.dominikbrodowski.net>
On Tue, Aug 08, 2017 at 09:36:14AM +0200, Dominik Brodowski wrote:
> On Tue, Aug 08, 2017 at 05:01:28PM +1000, NeilBrown wrote:
> > On Mon, Aug 07 2017, Dominik Brodowski wrote:
> >
> > > Neil, Shaohua,
> > >
> > > following up on David R's bug message: I have observed something similar
> > > on v4.12.[345] and v4.13-rc4, but not on v4.11. This is a RAID1 (on bare
> > > metal partitions, /dev/sdaX and /dev/sdbY linked together). In case it
> > > matters: Further upwards are cryptsetup, a DM volume group, then logical
> > > volumes, and then filesystems (ext4, but also happened with xfs).
> > >
> > > In a tedious bisect (the bug wasn't as quickly reproducible as I would like,
> > > but happened when I repeatedly created large lvs and filled them with some
> > > content, while compiling kernels in parallel), I was able to track this
> > > down to:
> > >
> > >
> > > commit 4ad23a976413aa57fe5ba7a25953dc35ccca5b71
> > > Author: NeilBrown <neilb@suse.com>
> > > Date: Wed Mar 15 14:05:14 2017 +1100
> > >
> > > MD: use per-cpu counter for writes_pending
> > >
> > > The 'writes_pending' counter is used to determine when the
> > > array is stable so that it can be marked in the superblock
> > > as "Clean". Consequently it needs to be updated frequently
> > > but only checked for zero occasionally. Recent changes to
> > > raid5 cause the count to be updated even more often - once
> > > per 4K rather than once per bio. This provided
> > > justification for making the updates more efficient.
> > >
> > > ...
> >
> > Thanks for the report... and for bisecting and for re-sending...
> >
> > I believe I have found the problem, and have sent a patch separately.
> >
> > If mddev->safemode == 1 and mddev->in_sync != 0, md_check_recovery()
> > causes the thread that calls it to spin.
> > Prior to the patch you found, that couldn't happen. Now it can,
> > so it needs to be handled more carefully.
> >
> > While I was examining the code, I found another bug - so that is a win!
> >
> > Thanks,
> > NeilBrown
>
>
> Nice catch. Thanks! Will give it (both patches at once) a try on the test
> system immediately.
More than 2 hours of stress-testing shows no issues any more. Very nice.
Thanks!
Dominik
next prev parent reply other threads:[~2017-08-08 9:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <ee7921d2-d3ff-2381-1f05-2c07b8001d08@unsolicited.net>
2017-08-06 17:37 ` RESEND: Crash with 4.12.4 kernel and high disk load (monthly RAID 6 check) David R
2017-08-07 11:20 ` [MD] Crash with 4.12+ kernel and high disk load -- bisected to 4ad23a976413: MD: use per-cpu counter for writes_pending Dominik Brodowski
2017-08-08 4:51 ` Shaohua Li
2017-08-08 6:55 ` David R
2017-08-08 7:01 ` David R
2017-08-08 7:04 ` NeilBrown
2017-08-08 7:10 ` Dominik Brodowski
2017-08-08 7:01 ` NeilBrown
2017-08-08 7:36 ` Dominik Brodowski
2017-08-08 9:06 ` Dominik Brodowski [this message]
2017-08-09 6:28 ` David R
2017-08-08 8:02 ` David R
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