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

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Message-ID: <CAOAMb1BWWzYPSode-6Y9+O5eNhMc-bYofCNwMRmzeC9-nhRb4g@mail.gmail.com>
Date:	Tue, 7 Aug 2012 17:53:49 +0900
From:	Chanho Min <chanho0207@...il.com>
To:	Bart Van Assche <bvanassche@....org>
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 Tue, Aug 7, 2012 at 2:56 AM, Bart Van Assche <bvanassche@....org> wrote:
> Indeed. How about the patch below ? Scsi devices are removed from
> starved_list after blk_cleanup_queue() and before put_device(). That
> guarantees that inside scsi_run_queue() get_device() under host lock
> will succeed.
Thanks, IMHO, it's harmless and the simple way to solve this issue.
But, I think the second half of your patches are not required, extra
referecne is might suffice?

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);
 }

 u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
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