[-mm patch] fix locking in __make_request (was Re: 2.6.20-mm2: Oops in generic_make_request)

[Frederik Deweerdt <deweerdt@free.fr>]

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On Sun, Feb 18, 2007 at 09:05:33PM +0100, Michal Piotrowski wrote:
> On 18/02/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> >On Sun, 18 Feb 2007 18:58:05 +0100 Mattia Dongili <malattia@linux.it> wrote:
> >
> >> On Sun, Feb 18, 2007 at 02:06:59PM +0100, Laurent Riffard wrote:
> >> > Le 18.02.2007 06:51, Andrew Morton a écrit :
> >> > >Temporarily at
> >> > >
> >> > >  http://userweb.kernel.org/~akpm/2.6.20-mm2/
> >> > >
> >> > >Will appear later at
> >> > >
> >> > > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.20/2.6.20-mm2/
> >> >
> >> > Hello, I've got a fully reproducible Oops. I just have to boot to
> >> > runlevel 2 and wait less than one minute.
> >>
> >> Maybe this oops is related too?
> >
> >Looks that way.
> >
Hi Michal,

This seems to be a locking problem in __make_request, check_plug_merge()
should be called with the q->queue_lock held.
Could you try the following patch? It silenced the oops for me.

Regards,
Frederik

Signed-off-by: Frederik Deweerdt <frederik.deweerdt@gmail.com>

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 577f448..666f34e 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -2919,14 +2919,14 @@ static int __make_request(request_queue_
 	 */
 	blk_queue_bounce(q, &bio);
 
+	spin_lock_irq(q->queue_lock);
 	/*
 	 * Check if we can merge with the plugged list before grabbing
 	 * any locks.
 	 */
 	if (!check_plug_merge(q, ioc, bio))
-		goto out;
+		goto out_unlock;
 
-	spin_lock_irq(q->queue_lock);
 	el_ret = elv_merge(q, &req, bio);
 	if (el_ret == ELEVATOR_BACK_MERGE) {
 		if (bio_attempt_back_merge(q, req, bio)) {
@@ -2984,7 +2984,6 @@ out_unlock:
 		list_add_tail(&req->queuelist, &ioc->plugged_list);
 	}
 
-out:
 	return 0;
 
 end_io_eopnotsupp: