Patch "scsi: sd: Do not override max_sectors_kb sysfs setting" has been added to the 4.9-stable tree

Patch "scsi: sd: Do not override max_sectors_kb sysfs setting" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    scsi: sd: Do not override max_sectors_kb sysfs setting

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     scsi-sd-do-not-override-max_sectors_kb-sysfs-setting.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 77082ca503bed061f7fbda7cfd7c93beda967a41 Mon Sep 17 00:00:00 2001
From: "Martin K. Petersen" <martin.petersen@oracle.com>
Date: Wed, 27 Sep 2017 21:38:59 -0400
Subject: scsi: sd: Do not override max_sectors_kb sysfs setting

From: Martin K. Petersen <martin.petersen@oracle.com>

commit 77082ca503bed061f7fbda7cfd7c93beda967a41 upstream.

A user may lower the max_sectors_kb setting in sysfs to accommodate
certain workloads. Previously we would always set the max I/O size to
either the block layer default or the optional preferred I/O size
reported by the device.

Keep the current heuristics for the initial setting of max_sectors_kb.
For subsequent invocations, only update the current queue limit if it
exceeds the capabilities of the hardware.

Reported-by: Don Brace <don.brace@microsemi.com>
Reviewed-by: Martin Wilck <mwilck@suse.com>
Tested-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/scsi/sd.c |   19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2867,8 +2867,6 @@ static int sd_revalidate_disk(struct gen
 		sd_read_write_same(sdkp, buffer);
 	}
 
-	sdkp->first_scan = 0;
-
 	/*
 	 * We now have all cache related info, determine how we deal
 	 * with flush requests.
@@ -2883,7 +2881,7 @@ static int sd_revalidate_disk(struct gen
 	q->limits.max_dev_sectors = logical_to_sectors(sdp, dev_max);
 
 	/*
-	 * Use the device's preferred I/O size for reads and writes
+	 * Determine the device's preferred I/O size for reads and writes
 	 * unless the reported value is unreasonably small, large, or
 	 * garbage.
 	 */
@@ -2897,8 +2895,19 @@ static int sd_revalidate_disk(struct gen
 		rw_max = min_not_zero(logical_to_sectors(sdp, dev_max),
 				      (sector_t)BLK_DEF_MAX_SECTORS);
 
-	/* Combine with controller limits */
-	q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));
+	/* Do not exceed controller limit */
+	rw_max = min(rw_max, queue_max_hw_sectors(q));
+
+	/*
+	 * Only update max_sectors if previously unset or if the current value
+	 * exceeds the capabilities of the hardware.
+	 */
+	if (sdkp->first_scan ||
+	    q->limits.max_sectors > q->limits.max_dev_sectors ||
+	    q->limits.max_sectors > q->limits.max_hw_sectors)
+		q->limits.max_sectors = rw_max;
+
+	sdkp->first_scan = 0;
 
 	set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity));
 	sd_config_write_same(sdkp);


Patches currently in stable-queue which might be from martin.petersen@oracle.com are

queue-4.9/scsi-sd-do-not-override-max_sectors_kb-sysfs-setting.patch