Re: [PATCH] scsi_lib: correctly retry failed zero length REQ_TYPE_FS commands

[Johannes Thumshirn <jthumshirn@suse.de>]

On Fri, May 13, 2016 at 12:04:06PM -0700, James Bottomley wrote:
> When SCSI was written, all commands coming from the filesystem
> (REQ_TYPE_FS commands) had data.  This meant that our signal for
> needing to complete the command was the number of bytes completed being
> equal to the number of bytes in the request.  Unfortunately, with the
> advent of flush barriers, we can now get zero length REQ_TYPE_FS
> commands, which confuse this logic because they satisfy the condition
> every time.  This means they never get retried even for retryable
> conditions, like UNIT ATTENTION because we complete them early assuming
> they're done.  Fix this by special casing the early completion
> condition to recognise zero length commands with errors and let them
> drop through to the retry code.
> 
> Reported-by: Sebastian Parschauer <s.parschauer@gmx.de>
> Signed-off-by: James E.J. Bottomley <jejb@linux.vnet.ibm.com>
> 
> ---
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 8106515..f704d02 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -911,9 +911,12 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
>  	}
>  
>  	/*
> -	 * If we finished all bytes in the request we are done now.
> +	 * special case: failed zero length commands always need to
> +	 * drop down into the retry code. Otherwise, if we finished
> +	 * all bytes in the request we are done now.
>  	 */
> -	if (!scsi_end_request(req, error, good_bytes, 0))
> +	if (!(blk_rq_bytes(req) == 0 && error) &&
> +	    !scsi_end_request(req, error, good_bytes, 0))
>  		return;


Naive question, why aren't we checking for blk_rq_bytes(req) == 0 && error in
scsi_end_request()?

>  
>  	/*
> --
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Johannes Thumshirn                                          Storage
jthumshirn@suse.de                                +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html