linux-kernel - Re: [PATCH] fix NULL-pointer dereference on scsi_run

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Message-ID: <5020E334.4070809@acm.org>
Date:	Tue, 07 Aug 2012 09:43:16 +0000
From:	Bart Van Assche <bvanassche@....org>
To:	Chanho Min <chanho0207@...il.com>
CC:	Mike Christie <michaelc@...wisc.edu>,
	James Bottomley <JBottomley@...allels.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] fix NULL-pointer dereference on scsi_run_queue

On 08/07/12 08:53, Chanho Min wrote:
> In addition, Is it ironic that we are careful to use put_device at
> scsi_request_fn?. If we trigger the ->remove(),
> It occur a oops. What about the removal of unlock/lock as patch bellow?
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 4037fd5..8d9eccd 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1608,11 +1608,7 @@ out_delay:
>         if (sdev->device_busy == 0)
>                 blk_delay_queue(q, SCSI_QUEUE_DELAY);
>  out:
> -       /* must be careful here...if we trigger the ->remove() function
> -        * we cannot be holding the q lock */
> -       spin_unlock_irq(q->queue_lock);
>         put_device(&sdev->sdev_gendev);
> -       spin_lock_irq(q->queue_lock);
>  }

As far as I can see the comment in the above code was added before
scsi_device_dev_release() was moved to user context, so it might be
outdated. See also
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=65110b2168950a19cc78b5027ed18cb811fbdae8.

Bart.
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