[Vivid][PATCH] sd: Fix max transfer length for 4k disks

[Chris J Arges]

From: Brian King <brking at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1418339

The following patch fixes an issue observed with 4k sector disks
where the max_hw_sectors attribute was getting set too large in
sd_revalidate_disk. Since sdkp->max_xfer_blocks is in units
of SCSI logical blocks and queue_max_hw_sectors is in units of
512 byte blocks, on a 4k sector disk, every time we went through
sd_revalidate_disk, we were taking the current value of
queue_max_hw_sectors and increasing it by a factor of 8. Fix
this by only shifting sdkp->max_xfer_blocks.

Cc: stable at vger.kernel.org
Signed-off-by: Brian King <brking at linux.vnet.ibm.com>
Reviewed-by: Paolo Bonzini <pbonzini at redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen at oracle.com>
Signed-off-by: Christoph Hellwig <hch at lst.de>
(cherry picked from commit 3a9794d32984b67a6d8992226918618f0e51e5d5)
Signed-off-by: Chris J Arges <chris.j.arges at canonical.com>
---
 drivers/scsi/sd.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index cfba74c..dd8c8d6 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2818,9 +2818,11 @@ static int sd_revalidate_disk(struct gendisk *disk)
 	 */
 	sd_set_flush_flag(sdkp);
 
-	max_xfer = min_not_zero(queue_max_hw_sectors(sdkp->disk->queue),
-				sdkp->max_xfer_blocks);
+	max_xfer = sdkp->max_xfer_blocks;
 	max_xfer <<= ilog2(sdp->sector_size) - 9;
+
+	max_xfer = min_not_zero(queue_max_hw_sectors(sdkp->disk->queue),
+				max_xfer);
 	blk_queue_max_hw_sectors(sdkp->disk->queue, max_xfer);
 	set_capacity(disk, sdkp->capacity);
 	sd_config_write_same(sdkp);
-- 
1.9.1