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Date: Thu, 20 Jan 2011 17:18:22 +0200
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <jaxboe@fusionio.com>,
        Philipp Reisner <philipp.reisner@linbit.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Lars Ellenberg <lars.ellenberg@linbit.com>,
        "Stephen M. Cameron" <scameron@beardog.cce.hp.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] loop: queue_lock NULL pointer derefence in
 blk_throtl_exit (v2)
Message-ID: <20110120151738.GA4665@swordfish.minsk.epam.com>
References: <20110114192532.GA4274@swordfish>
 <20110120113211.GB16184@redhat.com>
 <20110120125849.GA4172@swordfish>
 <20110120143546.GA18875@redhat.com>
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On (01/20/11 09:35), Vivek Goyal wrote:
> Hi Sergey,
>

Hi Vivek,

> Can we expand a little bit on comment that why do we need to have
> q->queue_lock initialized here now. Basically in the past nobody tried
> to take q->queue_lock in blk_cleanup_queue() path hence things just
> worked. Now blk throttling code is new and it takes q->queue_lock hence we
> run into issues. This could be true for some other future code too.
>=20
> Secondly currently blk throttle code seems to be the only user dependent
> on this lock initialization. So it might make sense to move this code
> closer to the actual call and blk_release_queue() might be even better
> place to do it atleast for now.
>=20

I'm afraid it's not safe to move NULL-check-and-fix out from blk_cleanup_qu=
eue,=20
since we're performing elevator_exit(q->elevator) call, which may depend on=
=20
q->queue_lock. For example, (./cfq-iosched.c: .elevator_exit_fn =3D cfq_exi=
t_queue)
cfq_exit_queue uses q->queue_lock.


	Sergey

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