linux-kernel - [PATCH AUTOSEL for 4.14 063/100] Btrfs: disable FUA if mounted with nobarrier

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Date:   Sun, 28 Jan 2018 22:26:40 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Omar Sandoval <osandov@...com>, David Sterba <dsterba@...e.com>,
        "Sasha Levin" <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.14 063/100] Btrfs: disable FUA if mounted with
 nobarrier

From: Omar Sandoval <osandov@...com>

[ 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.

Fixes: 387125fc722a8ed ("Btrfs: fix barrier flushes")
Signed-off-by: Omar Sandoval <osandov@...com>
Reviewed-by: Qu Wenruo <wqu@...e.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 fs/btrfs/disk-io.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index dfdab849037b..167ce43cabe8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3391,6 +3391,7 @@ static int write_dev_supers(struct btrfs_device *device,
 	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_device *device,
 		 * 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++;
 	}
-- 
2.11.0