Recent mmotms give me WARNING: at fs/namespace.c:612 mntput_no_expire()+...

when unmounting: __mntput()'s WARN_ON(count_mnt_writers(mnt)).

That's because vfs-optimize-touch_time-too.patch inverted the sense
of mnt_want_write_file(), which is error-returning, not a boolean.

Presumably filetime updates went missing too, but I didn't notice those.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Valerie Aurora <vaurora@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/inode.c

@@ -1478,7 +1478,7 @@ void file_update_time(struct file *file)
 		return;
 
 	/* Finally allowed to write? Takes lock. */
-	if (!mnt_want_write_file(file))
+	if (mnt_want_write_file(file))
 		return;
 
 	/* Only change inode inside the lock region */