Re: [patch 04/38] [SCSI] put stricter guards on queue deadchecks

[Jim Schutt]

Hi Greg,

Greg KH wrote:
> 2.6.38-stable review patch.  If anyone has any objections, please let us know.

You probably don't want to add this patch to stable kernels
until commit c055f5b2614b4f from
  git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-rc-fixes-2.6
shows up in Linus' tree.

See details in http://www.spinics.net/lists/kernel/msg1181665.html.

-- Jim


> ------------------
>
> From: James Bottomley <James.Bottomley@xxxxxxx>
>
> commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b upstream.
>
> SCSI uses request_queue->queuedata == NULL as a signal that the queue
> is dying.  We set this state in the sdev release function.  However,
> this allows a small window where we release the last reference but
> haven't quite got to this stage yet and so something will try to take
> a reference in scsi_request_fn and oops.  It's very rare, but we had a
> report here, so we're pushing this as a bug fix
>
> The actual fix is to set request_queue->queuedata to NULL in
> scsi_remove_device() before we drop the reference.  This causes
> correct automatic rejects from scsi_request_fn as people who hold
> additional references try to submit work and prevents anything from
> getting a new reference to the sdev that way.
>
> Signed-off-by: James Bottomley <James.Bottomley@xxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
>
> ---
>  drivers/scsi/scsi_sysfs.c |   16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -322,14 +322,8 @@ static void scsi_device_dev_release_user
>  		kfree(evt);
>  	}
>  
> -	if (sdev->request_queue) {
> -		sdev->request_queue->queuedata = NULL;
> -		/* user context needed to free queue */
> -		scsi_free_queue(sdev->request_queue);
> -		/* temporary expedient, try to catch use of queue lock
> -		 * after free of sdev */
> -		sdev->request_queue = NULL;
> -	}
> +	/* NULL queue means the device can't be used */
> +	sdev->request_queue = NULL;
>  
>  	scsi_target_reap(scsi_target(sdev));
>  
> @@ -937,6 +931,12 @@ void __scsi_remove_device(struct scsi_de
>  	if (sdev->host->hostt->slave_destroy)
>  		sdev->host->hostt->slave_destroy(sdev);
>  	transport_destroy_device(dev);
> +
> +	/* cause the request function to reject all I/O requests */
> +	sdev->request_queue->queuedata = NULL;
> +
> +	/* Freeing the queue signals to block that we're done */
> +	scsi_free_queue(sdev->request_queue);
>  	put_device(dev);
>  }
>  
>
>
> --
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