linux-kernel - [PATCH] scsi: sd: Keep the discard mode stable

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Date: Sat, 15 Jun 2024 00:03:47 +0800
From: Li Feng <fengli@...rtx.com>
To: "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
	linux-kernel@...r.kernel.org (open list),
	linux-scsi@...r.kernel.org (open list:SCSI SUBSYSTEM),
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: [PATCH] scsi: sd: Keep the discard mode stable

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@...rtx.com>
---
 drivers/scsi/sd.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index f6c822c9cbd2..0165dc70a99b 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2598,7 +2598,12 @@ 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, SD_LBP_WS16);
+		/*
+		 * When the discard mode has been set to UNMAP, it should not be set to
+		 * WRITE SAME with UNMAP.
+		 */
+		if (!sdkp->max_unmap_blocks)
+			sd_config_discard(sdkp, SD_LBP_WS16);
 	}

 	sdkp->capacity = lba + 1;
-- 
2.45.2