[PATCH 5.10/5.15 v2] scsi: sd: Revert "scsi: sd: Remove a local variable"

[PATCH 5.10/5.15 v2] scsi: sd: Revert "scsi: sd: Remove a local variable"

[Yu Kuai]

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;
 }
-- 
2.31.1

Re: [PATCH 5.10/5.15 v2] scsi: sd: Revert "scsi: sd: Remove a local variable"

[Greg KH]

On Tue, Nov 01, 2022 at 09:31:24AM +0800, Yu Kuai wrote:
> 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.

Now queued up, thanks.

greg k-h

Re: Patch "scsi: sd: Revert "scsi: sd: Remove a local variable"" has been added to the 4.14-stable tree

[Greg KH]

On Tue, Nov 01, 2022 at 08:35:22PM +0100, gregkh@linuxfoundation.org wrote:
> 
> This is a note to let you know that I've just added the patch titled
> 
>     scsi: sd: Revert "scsi: sd: Remove a local variable"
> 
> to the 4.14-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

Oops, nope, not 4.14, sorry for the noise, now dropped from there.

greg k-h