From: Yu Kuai yukuai3@huawei.com

This reverts commit 84f7a9de0602704bbec774a6c7f7c8c4994bee9c.

Because it introduces a problem that rq->__data_len is set to the wrong value.

before the patch: 1) nr_bytes = rq->__data_len 2) rq->__data_len = sdp->sector_size 3) scsi_init_io() 4) rq->__data_len = nr_bytes

after the patch: 1) rq->__data_len = sdp->sector_size 2) scsi_init_io() 3) rq->__data_len = rq->__data_len -> __data_len is wrong

It will cause that io can only complete one segment each time, and the io will requeue in scsi_io_completion_action(), which will cause severe performance degradation.

Scsi write same is removed in commit e383e16e84e9 ("scsi: sd: Remove WRITE_SAME support") from mainline, hence this patch is only needed for stable kernels.

Fixes: 84f7a9de0602 ("scsi: sd: Remove a local variable") Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Bart Van Assche bvanassche@acm.org ---

Changes in v2: - add description that this patch is only needed for stable kernels.

drivers/scsi/sd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index de6640ad1943..1e887c11e83d 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -1072,6 +1072,7 @@ static blk_status_t sd_setup_write_same_cmnd(struct scsi_cmnd *cmd) struct bio *bio = rq->bio; u64 lba = sectors_to_logical(sdp, blk_rq_pos(rq)); u32 nr_blocks = sectors_to_logical(sdp, blk_rq_sectors(rq)); + unsigned int nr_bytes = blk_rq_bytes(rq); blk_status_t ret;

if (sdkp->device->no_write_same) @@ -1108,7 +1109,7 @@ static blk_status_t sd_setup_write_same_cmnd(struct scsi_cmnd *cmd) */ rq->__data_len = sdp->sector_size; ret = scsi_alloc_sgtables(cmd); - rq->__data_len = blk_rq_bytes(rq); + rq->__data_len = nr_bytes;

return ret; }