Re: 2.6.39-rc5+ BUG at scsi_run_queue+0x24/0xe3

[Jim Schutt]

James Bottomley wrote:
> On Tue, 2011-05-03 at 11:27 -0600, Jim Schutt wrote:
> > James Bottomley wrote:
> > > On Tue, 2011-05-03 at 10:53 -0600, Jim Schutt wrote:
> > > > Please let me know if what further information you need, or if there is
> > > > anything I can do, to help resolve this.
> > > I think this is the fix (already in rc-fixes):
> > >
> > > James
> > >
> > > ---
> > > From 3e85ea868dbd60a84240be5c1eebc36841b9c568 Mon Sep 17 00:00:00 2001
> > > From: James Bottomley <James.Bottomley@xxxxxxx>
> > > Date: Sun, 1 May 2011 09:42:07 -0500
> > > Subject: [PATCH] [SCSI] fix oops in scsi_run_queue()
> > >
> > > The recent commit closing the race window in device teardown:
> > >
> > > commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
> > > Author: James Bottomley <James.Bottomley@xxxxxxx>
> > > Date:   Fri Apr 22 10:39:59 2011 -0500
> > >
> > >     [SCSI] put stricter guards on queue dead checks
> > >
> > > is causing a potential NULL deref in scsi_run_queue() because the
> > > q->queuedata may already be NULL by the time this function is called.
> > > Since we shouldn't be running a queue that is being torn down, simply
> > > add a NULL check in scsi_run_queue() to forestall this.
> > >
> > > Signed-off-by: James Bottomley <James.Bottomley@xxxxxxx>
> > >
> > > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> > > index e9901b8..03979f4 100644
> > > --- a/drivers/scsi/scsi_lib.c
> > > +++ b/drivers/scsi/scsi_lib.c
> > > @@ -404,6 +404,10 @@ static void scsi_run_queue(struct request_queue *q)
> > >  	LIST_HEAD(starved_list);
> > >  	unsigned long flags;
> > >  
> > > +	/* if the device is dead, sdev will be NULL, so no queue to run */
> > > +	if (!sdev)
> > > +		return;
> > > +
> > >  	if (scsi_target(sdev)->single_lun)
> > >  		scsi_single_lun_run(sdev);
> > >  
> > Hmmm, with the above added, I still get BUGs.  Here's an
> > example:
> >
> > [   17.142931] BUG: unable to handle kernel NULL pointer dereference at           (null)
> > [   17.143002] IP: [<ffffffffa01cf8c5>] scsi_run_queue+0x24/0xec [scsi_mod]
>
> Ooh, compiler optimisation, I think; try this instead
>
> James
>
> ---
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index e9901b8..0bac91e 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -400,10 +400,15 @@ static inline int scsi_host_is_busy(struct Scsi_Host *shost)
>  static void scsi_run_queue(struct request_queue *q)
>  {
>  	struct scsi_device *sdev = q->queuedata;
> -	struct Scsi_Host *shost = sdev->host;
> +	struct Scsi_Host *shost;
>  	LIST_HEAD(starved_list);
>  	unsigned long flags;
>  
> +	/* if the device is dead, sdev will be NULL, so no queue to run */
> +	if (!sdev)
> +		return;
> +
> +	shost = sdev->host;
>  	if (scsi_target(sdev)->single_lun)
>  		scsi_single_lun_run(sdev);
>  

Yes, that definitely fixes things for me.

Thanks!!

-- Jim

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