linux-kernel - [PATCH v2 5/5] btrfs: ensure that metadata and flush are issued from the root cgroup

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Date:   Tue, 10 Oct 2017 09:43:26 -0700
From:   Tejun Heo <tj@...nel.org>
To:     jack@...e.cz, axboe@...nel.dk, clm@...com, jbacik@...com
Cc:     kernel-team@...com, linux-kernel@...r.kernel.org,
        linux-btrfs@...r.kernel.org
Subject: [PATCH v2 5/5] btrfs: ensure that metadata and flush are issued from
 the root cgroup

>From 3bbed8c7747739cda48f592f165e8839da076a3a Mon Sep 17 00:00:00 2001

Issuing metdata or otherwise shared IOs from !root cgroup can lead to
priority inversion.  This patch ensures that those IOs are always
issued from the root cgroup.

This patch updates btrfs_update_iflags() to not set S_CGROUPWB on
btree_inodes.  This isn't strictly necessary as those inodes don't
call the function during init; however, this serves as documentation
and prevents possible future mistakes.  If this isn't desirable,
please feel free to drop the section.

v2: Fixed missing @bh in submit_bh_blkcg_css() call.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Chris Mason <clm@...com>
Cc: Josef Bacik <jbacik@...com>
---
 fs/btrfs/check-integrity.c | 2 +-
 fs/btrfs/disk-io.c         | 4 ++++
 fs/btrfs/ioctl.c           | 4 +++-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 7d5a9b5..d66774e 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -2741,7 +2741,7 @@ int btrfsic_submit_bh(int op, int op_flags, struct buffer_head *bh)
 	struct btrfsic_dev_state *dev_state;
 
 	if (!btrfsic_is_initialized)
-		return submit_bh(op, op_flags, bh);
+		return submit_bh_blkcg_css(op, op_flags, bh, blkcg_root_css);
 
 	mutex_lock(&btrfsic_mutex);
 	/* since btrfsic_submit_bh() might also be called before
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index dfdab84..fe8bbe1 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1025,6 +1025,8 @@ static blk_status_t btree_submit_bio_hook(void *private_data, struct bio *bio,
 	int async = check_async_write(bio_flags);
 	blk_status_t ret;
 
+	bio_associate_blkcg(bio, blkcg_root_css);
+
 	if (bio_op(bio) != REQ_OP_WRITE) {
 		/*
 		 * called for a read, do the setup so that checksum validation
@@ -3512,6 +3514,8 @@ static void write_dev_flush(struct btrfs_device *device)
 		return;
 
 	bio_reset(bio);
+	bio_associate_blkcg(bio, blkcg_root_css);
+
 	bio->bi_end_io = btrfs_end_empty_barrier;
 	bio_set_dev(bio, device->bdev);
 	bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_PREFLUSH;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 117cc63..8a7db6c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -150,7 +150,9 @@ void btrfs_update_iflags(struct inode *inode)
 		new_fl |= S_NOATIME;
 	if (ip->flags & BTRFS_INODE_DIRSYNC)
 		new_fl |= S_DIRSYNC;
-	new_fl |= S_CGROUPWB;
+	/* btree_inodes are always in the root cgroup */
+	if (btrfs_ino(ip) != BTRFS_BTREE_INODE_OBJECTID)
+		new_fl |= S_CGROUPWB;
 
 	set_mask_bits(&inode->i_flags,
 		      S_SYNC | S_APPEND | S_IMMUTABLE | S_NOATIME | S_DIRSYNC |
-- 
2.9.5