Re: [PATCH v2] scsi: sd: Optimal I/O size should be a multiple of physical block size

["Martin K. Petersen" <martin.petersen@oracle.com>]

Christoph?

> It was reported that some devices report an OPTIMAL TRANSFER LENGTH of
> 0xFFFF blocks. That looks bogus, especially for a device with a
> 4096-byte physical block size.
>
> Ignore OPTIMAL TRANSFER LENGTH if it is not a multiple of the device's
> reported physical block size.
>
> To make the sanity checking conditionals more readable--and to
> facilitate printing warnings--relocate the checking to a helper
> function. No functional change aside from the printks.
>
> Cc: <stable@vger.kernel.org>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199759
> Reported-by: Christoph Anton Mitterer <calestyo@scientia.net>
> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
>
> ---
>
> v2:
> 	- Added warnings as requested by hch
> 	- Moved the checks to a helper function
>
> Before:
>
> NAME ALIGNMENT MIN-IO   OPT-IO PHY-SEC LOG-SEC ROTA SCHED      RQ-SIZE  RA WSAME
> sda          0   4096 33553920    4096     512    0 mq-deadline    256 128   32M
>
> After:
>
> NAME ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED       RQ-SIZE   RA WSAME
> sda          0   4096      0    4096     512    0 mq-deadline     256 4096   32M
> ---
>  drivers/scsi/sd.c | 59 +++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 50 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 9aa409b38765..5dfe37b08d3b 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -3048,6 +3048,55 @@ static void sd_read_security(struct scsi_disk *sdkp, unsigned char *buffer)
>  		sdkp->security = 1;
>  }
>  
> +/*
> + * Determine the device's preferred I/O size for reads and writes
> + * unless the reported value is unreasonably small, large, not a
> + * multiple of the physical block size, or simply garbage.
> + */
> +static bool sd_validate_opt_xfer_size(struct scsi_disk *sdkp,
> +				      unsigned int dev_max)
> +{
> +	struct scsi_device *sdp = sdkp->device;
> +	unsigned int opt_xfer_bytes =
> +		logical_to_bytes(sdp, sdkp->opt_xfer_blocks);
> +
> +	if (sdkp->opt_xfer_blocks > dev_max) {
> +		sd_first_printk(KERN_WARNING, sdkp,
> +				"Optimal transfer size %u logical blocks " \
> +				"> dev_max (%u logical blocks)\n",
> +				sdkp->opt_xfer_blocks, dev_max);
> +		return false;
> +	}
> +
> +	if (sdkp->opt_xfer_blocks > SD_DEF_XFER_BLOCKS) {
> +		sd_first_printk(KERN_WARNING, sdkp,
> +				"Optimal transfer size %u logical blocks " \
> +				"> sd driver limit (%u logical blocks)\n",
> +				sdkp->opt_xfer_blocks, SD_DEF_XFER_BLOCKS);
> +		return false;
> +	}
> +
> +	if (opt_xfer_bytes < PAGE_SIZE) {
> +		sd_first_printk(KERN_WARNING, sdkp,
> +				"Optimal transfer size %u bytes < " \
> +				"PAGE_SIZE (%u bytes)\n",
> +				opt_xfer_bytes, (unsigned int)PAGE_SIZE);
> +		return false;
> +	}
> +
> +	if (opt_xfer_bytes & (sdkp->physical_block_size - 1)) {
> +		sd_first_printk(KERN_WARNING, sdkp,
> +				"Optimal transfer size %u bytes not a " \
> +				"multiple of physical block size (%u bytes)\n",
> +				opt_xfer_bytes, sdkp->physical_block_size);
> +		return false;
> +	}
> +
> +	sd_first_printk(KERN_INFO, sdkp, "Optimal transfer size %u bytes\n",
> +			opt_xfer_bytes);
> +	return true;
> +}
> +
>  /**
>   *	sd_revalidate_disk - called the first time a new disk is seen,
>   *	performs disk spin up, read_capacity, etc.
> @@ -3117,15 +3166,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
>  	dev_max = min_not_zero(dev_max, sdkp->max_xfer_blocks);
>  	q->limits.max_dev_sectors = logical_to_sectors(sdp, dev_max);
>  
> -	/*
> -	 * Determine the device's preferred I/O size for reads and writes
> -	 * 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 &&
> -	    logical_to_bytes(sdp, sdkp->opt_xfer_blocks) >= PAGE_SIZE) {
> +	if (sd_validate_opt_xfer_size(sdkp, dev_max)) {
>  		q->limits.io_opt = logical_to_bytes(sdp, sdkp->opt_xfer_blocks);
>  		rw_max = logical_to_sectors(sdp, sdkp->opt_xfer_blocks);
>  	} else

-- 
Martin K. Petersen	Oracle Linux Engineering