scsi: sd: Revert "scsi: sd: Remove a local variable"

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index de6640a..1e887c1 100644 (file)
--- 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;
 }