There is a scenario where a large number of discard commands
are issued when the iscsi initiator connects to the target
and then performs a session rescan operation. There is a time
window, most of the commands are in UNMAP mode, and some
discard commands become WRITE SAME with UNMAP.

The discard mode has been negotiated during the SCSI probe. If
the mode is temporarily changed from UNMAP to WRITE SAME with
UNMAP, IO ERROR may occur because the target may not implement
WRITE SAME with UNMAP. Keep the discard mode stable to fix this
issue.

Signed-off-by: Li Feng <fengli@smartx.com>
---
 drivers/scsi/sd.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index e01393ed4207..f628ca5ac0ac 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2621,8 +2621,6 @@ static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
 
 		if (buffer[14] & 0x40) /* LBPRZ */
 			sdkp->lbprz = 1;
-
-		sd_config_discard(sdkp, lim, SD_LBP_WS16);
 	}
 
 	sdkp->capacity = lba + 1;
@@ -3271,8 +3269,6 @@ static void sd_read_block_limits(struct scsi_disk *sdkp,
 		if (vpd->data[32] & 0x80)
 			sdkp->unmap_alignment =
 				get_unaligned_be32(&vpd->data[32]) & ~(1 << 31);
-
-		sd_config_discard(sdkp, lim, sd_discard_mode(sdkp));
 	}
 
  out:
@@ -3671,6 +3667,8 @@ static int sd_revalidate_disk(struct gendisk *disk)
 			sd_read_cpr(sdkp);
 		}
 
+		sd_config_discard(sdkp, &lim, sd_discard_mode(sdkp));
+
 		sd_print_capacity(sdkp, old_capacity);
 
 		sd_read_write_protect_flag(sdkp, buffer);
-- 
2.45.2

Li,

> The discard mode has been negotiated during the SCSI probe. If the
> mode is temporarily changed from UNMAP to WRITE SAME with UNMAP, IO
> ERROR may occur because the target may not implement WRITE SAME with
> UNMAP. Keep the discard mode stable to fix this issue.

This is fine with me. It's a subset of what I have pending in my
discovery series but it doesn't look like that will ready in time for
6.11. So let's just grab this for now.

Jens: Probably easiest if you take this through the block-limits branch.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

(note that this needs the for-6.11/block-limits branch to be pulled
into the scsi tree, which Martin agreed on, but which hasn't happened
yet)