LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Jens Axboe <jens.axboe@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>,
	Michal Piotrowski <michal.k.k.piotrowski@gmail.com>,
	Andrew Morton <akpm@osdl.org>, Neil Brown <neilb@cse.unsw.edu.au>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [patch-mm] Workaround for RAID breakage
Date: Tue, 16 Jan 2007 21:07:58 +1100	[thread overview]
Message-ID: <20070116100758.GC3938@kernel.dk> (raw)
In-Reply-To: <1168936038.2941.182.camel@localhost.localdomain>

On Tue, Jan 16 2007, Thomas Gleixner wrote:
> On Tue, 2007-01-16 at 11:41 +1100, Jens Axboe wrote:
> > > 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 ?
> > 
> > It should not go negative, that would be a bug elsewhere. So it's
> > interesting if it does, we should definitely put a WARN_ON() check in
> > there for that.
> 
> Well. All offenders come via queue_sync_plugs(). queue_sync_plugs()
> calls blk_unplug_current().

Ah, again a problem because the #plug branch wasn't pushed to #for-akpm
in due time. That problem was fixed already :/

> One path which triggers is blk_sync_queue(). This happens e.g. in the
> cleanup of the floppy check. There are other call pathes too.
> 
> The other is raid md_super_write(). It is not plugged and calls with the
> barrier bit set, which executes the unlikely path in __make_request():
> 
>         if (unlikely(bio_barrier(bio))) {
>                 queue_sync_plugs(q);
>                 spin_lock_irq(q->queue_lock);
>                 goto get_rq;
>         }
> 
> So you either need checks all over the place to avoid calling
> blk_unplug_current(), or you prevent the unplug below 0 like I did. The
> BUG_ON()s I added should catch any real invalid callers. But it's up to
> you.

blk_replug_current_nested() should do it. I'll make sure the branch is
updated for next -mm.

The BUG_ON()'s are indeed correct, they should just be moved further
down the function.

-- 
Jens Axboe


      reply	other threads:[~2007-01-16 10:08 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-12 13:33 2.6.20-rc4-mm1 md problem Michal Piotrowski
2007-01-12 15:52 ` Rafael J. Wysocki
2007-01-12 17:40   ` Michal Piotrowski
2007-01-12 17:58     ` Michal Piotrowski
2007-01-14 21:59       ` Jens Axboe
2007-01-15  7:17 ` Ingo Molnar
2007-01-15  8:08   ` Thomas Gleixner
2007-01-15 18:03     ` [patch-mm] Workaround for RAID breakage Thomas Gleixner
2007-01-15 20:17       ` Michal Piotrowski
2007-01-16  0:41       ` Jens Axboe
2007-01-16  8:27         ` Thomas Gleixner
2007-01-16 10:07           ` Jens Axboe [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20070116100758.GC3938@kernel.dk \
    --to=jens.axboe@oracle.com \
    --cc=akpm@osdl.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=michal.k.k.piotrowski@gmail.com \
    --cc=mingo@elte.hu \
    --cc=neilb@cse.unsw.edu.au \
    --cc=tglx@linutronix.de \
    --subject='Re: [patch-mm] Workaround for RAID breakage' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).