[PATCH 2/5] vfs: Move noop_backing_dev_info check from sync into writeback

[Jan Kara <jack@suse.cz>]

In principle, a filesystem may want to have ->sync_fs() called during sync(1)
although it does not have a bdi (i.e. s_bdi is set to noop_backing_dev_info).
Only writeback code really needs bdi set to something reasonable. So move the
checks where they are more logical.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/fs-writeback.c |    6 ++++++
 fs/sync.c         |    9 +--------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 0f015a0..82a876b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1194,6 +1194,9 @@ void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
 		.nr_pages	= nr,
 	};
 
+	/* Nothing to do? */
+	if (sb->s_bdi == &noop_backing_dev_info)
+		return;
 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 	bdi_queue_work(sb->s_bdi, &work);
 	wait_for_completion(&done);
@@ -1272,6 +1275,9 @@ void sync_inodes_sb(struct super_block *sb)
 		.done		= &done,
 	};
 
+	/* Nothing to do? */
+	if (sb->s_bdi == &noop_backing_dev_info)
+		return;
 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
 	bdi_queue_work(sb->s_bdi, &work);
diff --git a/fs/sync.c b/fs/sync.c
index f8f21d9..2f5bd52 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -63,13 +63,6 @@ int sync_filesystem(struct super_block *sb)
 	if (sb->s_flags & MS_RDONLY)
 		return 0;
 
-	/*
-	 * This should be safe, as we require bdi backing to actually
-	 * write out data in the first place.
-	 */
-	if (sb->s_bdi == &noop_backing_dev_info)
-		return 0;
-
 	__sync_filesystem(sb, 0);
 	ret = __sync_blockdev(sb->s_bdev, 0);
 	if (ret < 0)
@@ -82,7 +75,7 @@ EXPORT_SYMBOL_GPL(sync_filesystem);
 static void sync_one_sb(struct super_block *sb, void *arg)
 {
 	/* Avoid read-only filesystems and filesystems without backing device */
-	if (!(sb->s_flags & MS_RDONLY) && sb->s_bdi != &noop_backing_dev_info)
+	if (!(sb->s_flags & MS_RDONLY))
 		__sync_filesystem(sb, *(int *)arg);
 }
 /*
-- 
1.7.1