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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Ethan Lien" <ethanlien@synology.com>,
        "David Sterba" <dsterba@suse.com>,
        "Nikolay Borisov" <nborisov@suse.com>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
Message-ID: <lsq.1544392233.988994940@decadent.org.uk>
Subject: [PATCH 3.16 109/328] btrfs: use correct compare function of
 dirty_metadata_bytes
In-Reply-To: <lsq.1544392232.713909046@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ethan Lien <ethanlien@synology.com>

commit d814a49198eafa6163698bdd93961302f3a877a4 upstream.

We use customized, nodesize batch value to update dirty_metadata_bytes.
We should also use batch version of compare function or we will easily
goto fast path and get false result from percpu_counter_compare().

Fixes: e2d845211eda ("Btrfs: use percpu counter for dirty metadata count")
Signed-off-by: Ethan Lien <ethanlien@synology.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 3.16: In __btrfs_btree_balance_dirty(), use
 root->fs_info instead of fs_info]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/btrfs/disk-io.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -991,8 +991,9 @@ static int btree_writepages(struct addre
 
 		fs_info = BTRFS_I(mapping->host)->root->fs_info;
 		/* this is a bit racy, but that's ok */
-		ret = percpu_counter_compare(&fs_info->dirty_metadata_bytes,
-					     BTRFS_DIRTY_METADATA_THRESH);
+		ret = __percpu_counter_compare(&fs_info->dirty_metadata_bytes,
+					     BTRFS_DIRTY_METADATA_THRESH,
+					     fs_info->dirty_metadata_batch);
 		if (ret < 0)
 			return 0;
 	}
@@ -3793,8 +3794,9 @@ static void __btrfs_btree_balance_dirty(
 	if (flush_delayed)
 		btrfs_balance_delayed_items(root);
 
-	ret = percpu_counter_compare(&root->fs_info->dirty_metadata_bytes,
-				     BTRFS_DIRTY_METADATA_THRESH);
+	ret = __percpu_counter_compare(&root->fs_info->dirty_metadata_bytes,
+				     BTRFS_DIRTY_METADATA_THRESH,
+				     root->fs_info->dirty_metadata_batch);
 	if (ret > 0) {
 		balance_dirty_pages_ratelimited(
 				   root->fs_info->btree_inode->i_mapping);