Re: [PATCH] scsi: retry MODE SENSE on unit attention

[Ewan Milne <emilne@redhat.com>]

On Thu, 2015-06-11 at 13:01 +0200, Hannes Reinecke wrote:
> The 'sd' driver is calling scsi_mode_sense() to figure out
> internal details. But scsi_mode_sense() never checks for
> any pending unit attentions, so we're getting annoying error
> messages like:
> 
> MODE SENSE: unimplemented page/subpage: 0x00/0x00
> 
> and a possible wrong decision for device cache handling.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
>  drivers/scsi/scsi_lib.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 2428d96..d7915c8 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -2423,7 +2423,7 @@ scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
>  	unsigned char cmd[12];
>  	int use_10_for_ms;
>  	int header_length;
> -	int result;
> +	int result, retry_count = retries;
>  	struct scsi_sense_hdr my_sshdr;
>  
>  	memset(data, 0, sizeof(*data));
> @@ -2502,6 +2502,11 @@ scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
>  			data->block_descriptor_length = buffer[3];
>  		}
>  		data->header_length = header_length;
> +	} else if ((status_byte(result) == CHECK_CONDITION) &&
> +		   scsi_sense_valid(sshdr) &&
> +		   sshdr->sense_key == UNIT_ATTENTION && retry_count) {
> +		retry_count--;
> +		goto retry;
>  	}
>  
>  	return result;

Great, but shouldn't we be doing this more generally?  What about
scsi_mode_select()?

(And, with the number of status changes that can get reported by
 UAs, we might want to think about increasing the retry count on
 these commands up from 3 at some point.)

Reviewed-by: Ewan D. Milne <emilne@redhat.com>