Re: [PATCH 2/3] sd: Reject optimal transfer length smaller than page size

[Ewan Milne <emilne@redhat.com>]

On Wed, 2015-12-16 at 17:53 -0500, Martin K. Petersen wrote:
> Eryu Guan reported that loading scsi_debug would fail. This turned out
> to be caused by scsi_debug reporting an optimal I/O size of 32KB which
> is smaller than the 64KB page size on the PowerPC system in question.
> 
> Add a check to ensure that we only use the device-reported OPTIMAL
> TRANSFER LENGTH if it is bigger than or equal to the page cache size.
> 
> Reported-by: Eryu Guan <guaneryu@gmail.com>
> Reported-by: Ming Lei <tom.leiming@gmail.com>
> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
> ---
>  drivers/scsi/sd.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 3d22fc3e3c1a..4e08d1cd704d 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2885,10 +2885,13 @@ static int sd_revalidate_disk(struct gendisk *disk)
>  
>  	/*
>  	 * Use the device's preferred I/O size for reads and writes
> -	 * unless the reported value is unreasonably large (or garbage).
> +	 * unless the reported value is unreasonably small, large, or
> +	 * garbage.
>  	 */
> -	if (sdkp->opt_xfer_blocks && sdkp->opt_xfer_blocks <= dev_max &&
> -	    sdkp->opt_xfer_blocks <= SD_DEF_XFER_BLOCKS)
> +	if (sdkp->opt_xfer_blocks &&
> +	    sdkp->opt_xfer_blocks <= dev_max &&
> +	    sdkp->opt_xfer_blocks <= SD_DEF_XFER_BLOCKS &&
> +	    sdkp->opt_xfer_blocks * sdp->sector_size >= PAGE_CACHE_SIZE)
>  		rw_max = q->limits.io_opt =
>  			logical_to_sectors(sdp, sdkp->opt_xfer_blocks);
>  	else

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