linux-kernel - Re: CFQ is broken for CONFIG_BLK_CGROUP=y, CFQ_GROUP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100428154457.GC16033@redhat.com>
Date:	Wed, 28 Apr 2010 11:44:57 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: CFQ is broken for CONFIG_BLK_CGROUP=y, CFQ_GROUP_IOSCHED=n

On Wed, Apr 28, 2010 at 07:36:02PM +0400, Dmitry Monakhov wrote:
> Vivek Goyal <vgoyal@...hat.com> writes:
> 
> > On Wed, Apr 28, 2010 at 04:44:51PM +0400, Dmitry Monakhov wrote:
> >> 
> >> I've had an  oops on kernel boot due to NULL pointer deference
> >> linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6
> >> I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED
> >> In this case cfq_ref_get_cfqg() defined as 
> >> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
> >> {
> >>         return NULL;
> >> }
> >> So following call trace is simply NOOP
> >> cfq_set_request()
> >>  rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
> >> 
> >> Which later result in OOPS on bio insertion
> >> cfq_insert_request
> >>  -> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...)
> >>     -> spin_lock_irqsave(&blkg->stats_lock, flags);
> >> 
> >> Bad commit.
> >> >From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001
> >> From: Vivek Goyal <vgoyal@...hat.com>
> >> Date: Wed, 21 Apr 2010 17:44:16 +0200
> >> Subject: [PATCH] blkio: Fix blkio crash during rq stat update
> >
> > Dmitry, this patch should fix the issue. Can you please give it a try.
> Yes. the issue is gone.
> >
> > Jens, I know you don't like this form of cfq_ref_get_cfqg(), but this
> > seems to be the simplest solution to fix it.
> IMHO following fix is simpler, and cleaner.

> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 286008c..0f3eb70 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -1094,7 +1094,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
>  
>  static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
>  {
> -	return NULL;
> +	return cfqg;
>  }

Thanks Dmitry. I like it. simpler.

Vivek
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/