dcache: let the dentry count go down to zero without taking d_lock

We can be more aggressive about this, if we are clever and careful. This is subtle.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/lockref.h b/include/linux/lockref.h
index 4bfde0e..b10b122d 100644
--- a/include/linux/lockref.h
+++ b/include/linux/lockref.h
@@ -28,12 +28,13 @@
 #endif
 		struct {
 			spinlock_t lock;
-			unsigned int count;
+			int count;
 		};
 	};
 };
 
 extern void lockref_get(struct lockref *);
+extern int lockref_put_return(struct lockref *);
 extern int lockref_get_not_zero(struct lockref *);
 extern int lockref_get_or_lock(struct lockref *);
 extern int lockref_put_or_lock(struct lockref *);