From: Ivan Mironov <mironov.ivan@gmail.com>
Date: Sun, 23 Dec 2018 12:41:58 +0500
Subject: scsi: sd: Fix cache_type_store()
Git-commit: 44759979a49bfd2d20d789add7fa81a21eb1a4ab
Patch-mainline: v5.0-rc3
References: git-fixes

Changing of caching mode via /sys/devices/.../scsi_disk/.../cache_type may
fail if device responds to MODE SENSE command with DPOFUA flag set, and
then checks this flag to be not set on MODE SELECT command.

In this scenario, when trying to change cache_type, write always fails:

	# echo "none" >cache_type
	bash: echo: write error: Invalid argument

And following appears in dmesg:

	[13007.865745] sd 1:0:1:0: [sda] Sense Key : Illegal Request [current]
	[13007.865753] sd 1:0:1:0: [sda] Add. Sense: Invalid field in parameter list

>From SBC-4 r15, 6.5.1 "Mode pages overview", description of DEVICE-SPECIFIC
PARAMETER field in the mode parameter header:
	...
	The write protect (WP) bit for mode data sent with a MODE SELECT
	command shall be ignored by the device server.
	...
	The DPOFUA bit is reserved for mode data sent with a MODE SELECT
	command.
	...

The remaining bits in the DEVICE-SPECIFIC PARAMETER byte are also reserved
and shall be set to zero.

[mkp: shuffled commentary to commit description]

Cc: stable@vger.kernel.org
Signed-off-by: Ivan Mironov <mironov.ivan@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Lee Duncan <lduncan@suse.com>
---
 drivers/scsi/sd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index a1a44f52e0e8..b2da8a00ec33 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -206,6 +206,12 @@ cache_type_store(struct device *dev, struct device_attribute *attr,
 	sp = buffer_data[0] & 0x80 ? 1 : 0;
 	buffer_data[0] &= ~0x80;
 
+	/*
+	 * Ensure WP, DPOFUA, and RESERVED fields are cleared in
+	 * received mode parameter buffer before doing MODE SELECT.
+	 */
+	data.device_specific = 0;
+
 	if (scsi_mode_select(sdp, 1, sp, 8, buffer_data, len, SD_TIMEOUT,
 			     SD_MAX_RETRIES, &data, &sshdr)) {
 		if (scsi_sense_valid(&sshdr))