Re: [PATCH 1/1] [PATCH REGRESSION] alua: fix bus detach oops

[Hannes Reinecke <hare@suse.de>]

On 01/28/2015 10:46 AM, michaelc@cs.wisc.edu wrote:
> From: Mike Christie <michaelc@cs.wisc.edu>
> 
> This fixes a regression caused by commit
> 1d5203284d8acbdfdf9b478d434450b34f338f28
> 
> The bug is that the alua detach() callout will try to access the
> sddev->scsi_dh_data, but we have already set it to NULL. This patch
> moves the clearing of that field to after detach() is called.
> 
> It looks like the regression was added during 3.19 development,
> so it has not been in a released kernel, and so I did not cc
> stable.
> 
> Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
> 
> ---
>  drivers/scsi/device_handler/scsi_dh.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
> index 1dba62c..1efebc9 100644
> --- a/drivers/scsi/device_handler/scsi_dh.c
> +++ b/drivers/scsi/device_handler/scsi_dh.c
> @@ -136,11 +136,12 @@ static void __detach_handler (struct kref *kref)
>  	struct scsi_device_handler *scsi_dh = scsi_dh_data->scsi_dh;
>  	struct scsi_device *sdev = scsi_dh_data->sdev;
>  
> +	scsi_dh->detach(sdev);
> +
>  	spin_lock_irq(sdev->request_queue->queue_lock);
>  	sdev->scsi_dh_data = NULL;
>  	spin_unlock_irq(sdev->request_queue->queue_lock);
>  
> -	scsi_dh->detach(sdev);
>  	sdev_printk(KERN_NOTICE, sdev, "%s: Detached\n", scsi_dh->name);
>  	module_put(scsi_dh->module);
>  }
> 
Errm.

We save the contents first:

>  	struct scsi_device_handler *scsi_dh = scsi_dh_data->scsi_dh;

Then set the pointer to NULL:

>  	sdev->scsi_dh_data = NULL;

and then call 'detach':

> 	scsi_dh->detach(sdev);

So scsi_dh is _not_ NULL, hence it shouldn't oops.

NACK.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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