[PATCH v3 1/2] scsi: sd: Keep the discard mode stable

[Li Feng <fengli@smartx.com>]

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.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 8bb3a3611851..c180427e2c98 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2711,8 +2711,6 @@ 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;
@@ -3365,8 +3363,6 @@ static void sd_read_block_limits(struct scsi_disk *sdkp,
 			sdkp->unmap_alignment =
 				get_unaligned_be32(&vpd->data[32]) & ~(1 << 31);
 
-		sd_config_discard(sdkp, lim, sd_discard_mode(sdkp));
-
 config_atomic:
 		sdkp->max_atomic = get_unaligned_be32(&vpd->data[44]);
 		sdkp->atomic_alignment = get_unaligned_be32(&vpd->data[48]);
@@ -3756,6 +3752,8 @@ 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