vfs: fix unconditional write_super() call in file_fsync()

We need to check ->s_dirt before calling write_super().  It became the cause
of an unneeded write.

This bug was noticed by Sudhanshu Saxena.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/sync.c b/fs/sync.c
index 7cd005ea76390f385dc85af2c11e8121b6b4dd69..228e17b5e9ee911c2c2f58b4090e33b96954ff23 100644 (file)
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -64,7 +64,7 @@ int file_fsync(struct file *filp, struct dentry *dentry, int datasync)
        /* sync the superblock to buffers */
        sb = inode->i_sb;
        lock_super(sb);
-       if (sb->s_op->write_super)
+       if (sb->s_dirt && sb->s_op->write_super)
                sb->s_op->write_super(sb);
        unlock_super(sb);