[3.16.y-ckt stable] Patch "dm mirror: do not degrade the mirror on discard error" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    dm mirror: do not degrade the mirror on discard error

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 7d0556d0d5d9d1720886a3ab171f12949c03dc72 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka at redhat.com>
Date: Thu, 12 Feb 2015 10:09:20 -0500
Subject: dm mirror: do not degrade the mirror on discard error

commit f2ed51ac64611d717d1917820a01930174c2f236 upstream.

It may be possible that a device claims discard support but it rejects
discards with -EOPNOTSUPP.  It happens when using loopback on ext2/ext3
filesystem driven by the ext4 driver.  It may also happen if the
underlying devices are moved from one disk on another.

If discard error happens, we reject the bio with -EOPNOTSUPP, but we do
not degrade the array.

This patch fixes failed test shell/lvconvert-repair-transient.sh in the
lvm2 testsuite if the testsuite is extracted on an ext2 or ext3
filesystem and it is being driven by the ext4 driver.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/md/dm-raid1.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 7dfdb5c746d6..089d62751f7f 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -604,6 +604,15 @@ static void write_callback(unsigned long error, void *context)
 		return;
 	}

+	/*
+	 * If the bio is discard, return an error, but do not
+	 * degrade the array.
+	 */
+	if (bio->bi_rw & REQ_DISCARD) {
+		bio_endio(bio, -EOPNOTSUPP);
+		return;
+	}
+
 	for (i = 0; i < ms->nr_mirrors; i++)
 		if (test_bit(i, &error))
 			fail_mirror(ms->mirror + i, DM_RAID1_WRITE_ERROR);