Patch "Btrfs: disable FUA if mounted with nobarrier" has been added to the 4.14-stable tree

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

Btrfs: disable FUA if mounted with nobarrier

to the 4.14-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:
btrfs-disable-fua-if-mounted-with-nobarrier.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Omar Sandoval <[email protected]>
Date: Tue, 5 Dec 2017 22:54:02 -0800
Subject: Btrfs: disable FUA if mounted with nobarrier

From: Omar Sandoval <[email protected]>

[ Upstream commit 1b9e619c5bc8235cfba3dc4ced2fb0e3554a05d4 ]

I was seeing disk flushes still happening when I mounted a Btrfs filesystem with nobarrier for testing. This is because we use FUA to write out the first super block, and on devices without FUA support, the block layer translates FUA to a flush. Even on devices supporting true FUA, using FUA when we asked for no barriers is surprising.

---
 fs/btrfs/disk-io.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

@@ -3391,6 +3391,7 @@ static int write_dev_supers(struct btrfs
 	int errors = 0;
 	u32 crc;
 	u64 bytenr;
+	int op_flags;
 
 	if (max_mirrors == 0)
 		max_mirrors = BTRFS_SUPER_MIRROR_MAX;

@@ -3433,13 +3434,10 @@ static int write_dev_supers(struct btrfs
 		 * we fua the first super.  The others we allow
 		 * to go down lazy.
 		 */
-		if (i == 0) {
-			ret = btrfsic_submit_bh(REQ_OP_WRITE,
-				REQ_SYNC | REQ_FUA | REQ_META | REQ_PRIO, bh);
-		} else {
-			ret = btrfsic_submit_bh(REQ_OP_WRITE,
-				REQ_SYNC | REQ_META | REQ_PRIO, bh);
-		}
+		op_flags = REQ_SYNC | REQ_META | REQ_PRIO;
+		if (i == 0 && !btrfs_test_opt(device->fs_info, NOBARRIER))
+			op_flags |= REQ_FUA;
+		ret = btrfsic_submit_bh(REQ_OP_WRITE, op_flags, bh);
 		if (ret)
 			errors++;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/btrfs-disable-fua-if-mounted-with-nobarrier.patch