linux-kernel - Re: [patch-mm] Workaround for RAID breakage

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Message-ID: <6bffcb0e0701151217w3b20d24q9df0a54f0a65b99@mail.gmail.com>
Date:	Mon, 15 Jan 2007 21:17:30 +0100
From:	"Michal Piotrowski" <michal.k.k.piotrowski@...il.com>
To:	tglx@...utronix.de
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Andrew Morton" <akpm@...l.org>,
	"Neil Brown" <neilb@....unsw.edu.au>,
	LKML <linux-kernel@...r.kernel.org>,
	"Jens Axboe" <jens.axboe@...cle.com>
Subject: Re: [patch-mm] Workaround for RAID breakage

On 15/01/07, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Mon, 2007-01-15 at 09:08 +0100, Thomas Gleixner wrote:
> > > Thomas saw something similar yesterday and he the partial results that
> > > git.block (between rc2-mm1 and rc4-mm1) breaks certain disk drivers or
> > > filesystems drivers. For me it worked fine, so it must be only on some
> > > combinations. The changes to ll_rw_block.c look quite extensive.
> >
> > Yes. Jens Axboe confirmed yesterday that the plug changes broke RAID.
>
> I tracked this down and found two problems:
>
> - The new plug/unplug code does not check for underruns. That allows the
> plug count (ioc->plugged) to become negative. This gets triggered from
> various places.
>
> AFAICS this is intentional to avoid checks all over the place, but the
> underflow check is missing. All we need to do is make sure, that in case
> of ioc->plugged == 0 we return early and bug, if there is either a queue
> plugged in or the plugged_list is not empty.
>
> Jens ?
>
> - The raid1 code has no bitmap set in remount r/w. So the
> pending_bio_list gets not processed for quite a time. The workaround is
> to kick mddev->thread, so the list is processed. Not sure about that.
>
> Neil ?
>
> At least it boots and behaves normal.

Yes, it works fine now. Thanks!

>         tglx

Regards,
Michal

-- 
Michal K. K. Piotrowski
LTG - Linux Testers Group
(http://www.stardust.webpages.pl/ltg/)
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