vfs: Move noop_backing_dev_info check from sync into writeback

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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 41a3ccff18d8..8f660dd6137a 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1315,6 +1315,8 @@ void writeback_inodes_sb_nr(struct super_block *sb,
                 .reason                 = reason,
         };
 
+        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);
@@ -1398,6 +1400,9 @@ void sync_inodes_sb(struct super_block *sb)
                 .reason         = WB_REASON_SYNC,
         };
 
+        /* 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);