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

Frederik Deweerdt
2007-02-19T13:05:05Z

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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;