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

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Message-ID: <50213F56.7030609@cs.wisc.edu>
Date:	Tue, 07 Aug 2012 11:16:22 -0500
From:	Mike Christie <michaelc@...wisc.edu>
To:	Bart Van Assche <bvanassche@....org>
CC:	Chanho Min <chanho0207@...il.com>,
	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 08/06/2012 12:56 PM, Bart Van Assche wrote:
> On 08/04/12 22:36, Mike Christie wrote:
>> On 08/04/2012 03:18 PM, Bart Van Assche wrote:
>>> On 08/04/12 16:46, Mike Christie wrote:
>>>> I think we have to have scsi-ml do a get_device when a sdev is added to
>>>> the starved entry and then do a put_device when it is removed (must do
>>>> these under the host lock for the starved entry case too). I am not sure
>>>> if that is just a hack/papering-over of the problem and there are more
>>>> issues like this.
>>>
>>> That would result in a more complex patch than the patch at the start of
>>> this thread, isn't it ?
>>
>> Yaah, but the original patch in this thread is still racey isn't it?
> 
> 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.
> 
> ---
>  drivers/scsi/scsi_lib.c   |    5 +++++
>  drivers/scsi/scsi_sysfs.c |    7 ++++++-
>  2 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index ffd7773..bd7daec 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -452,10 +452,15 @@ static void scsi_run_queue(struct request_queue *q)
>  			continue;
>  		}
>  
> +		get_device(&sdev->sdev_gendev);
>  		spin_unlock(shost->host_lock);
> +
>  		spin_lock(sdev->request_queue->queue_lock);
>  		__blk_run_queue(sdev->request_queue);
>  		spin_unlock(sdev->request_queue->queue_lock);
> +
> +		put_device(&sdev->sdev_gendev);
> +
>  		spin_lock(shost->host_lock);
>  	}
>  	/* put any unprocessed entries back */
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 093d4f6..44f232e 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -348,7 +348,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
>  	starget->reap_ref++;
>  	list_del(&sdev->siblings);
>  	list_del(&sdev->same_target_siblings);
> -	list_del(&sdev->starved_entry);
>  	spin_unlock_irqrestore(sdev->host->host_lock, flags);
>  
>  	cancel_work_sync(&sdev->event_work);
> @@ -956,6 +955,8 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev)
>  void __scsi_remove_device(struct scsi_device *sdev)
>  {
>  	struct device *dev = &sdev->sdev_gendev;
> +	struct Scsi_Host *shost = sdev->host;
> +	unsigned long flags;
>  
>  	if (sdev->is_visible) {
>  		if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0)
> @@ -977,6 +978,10 @@ void __scsi_remove_device(struct scsi_device *sdev)
>  	blk_cleanup_queue(sdev->request_queue);
>  	cancel_work_sync(&sdev->requeue_work);
>  
> +	spin_lock_irqsave(shost->host_lock, flags);
> +	list_del(&sdev->starved_entry);
> +	spin_unlock_irqrestore(shost->host_lock, flags);
> +
>  	if (sdev->host->hostt->slave_destroy)
>  		sdev->host->hostt->slave_destroy(sdev);
>  	transport_destroy_device(dev);
> 

I think the patch will work now.

Reviewed-by: Mike Christie <michaelc@...wisc.edu>
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