make retain_dentry() neutral with respect to refcounting

retain_dentry() used to decrement refcount if and only if it returned
true.  Lift those decrements into the callers.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

fs/dcache.c

@@ -680,7 +680,6 @@ static inline bool retain_dentry(struct dentry *dentry)
 		return false;
 
 	/* retain; LRU fodder */
-	dentry->d_lockref.count--;
 	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
 		d_lru_add(dentry);
 	else if (unlikely(!(dentry->d_flags & DCACHE_REFERENCED)))
@@ -744,6 +743,8 @@ static struct dentry *dentry_kill(struct dentry *dentry)
 	} else if (likely(!retain_dentry(dentry))) {
 		__dentry_kill(dentry);
 		return parent;
+	} else {
+		dentry->d_lockref.count--;
 	}
 	/* we are keeping it, after all */
 	if (inode)
@@ -893,6 +894,7 @@ void dput(struct dentry *dentry)
 		rcu_read_unlock();
 
 		if (likely(retain_dentry(dentry))) {
+			dentry->d_lockref.count--;
 			spin_unlock(&dentry->d_lock);
 			return;
 		}
@@ -925,6 +927,8 @@ void dput_to_list(struct dentry *dentry, struct list_head *list)
 	if (!retain_dentry(dentry)) {
 		--dentry->d_lockref.count;
 		to_shrink_list(dentry, list);
+	} else {
+		--dentry->d_lockref.count;
 	}
 	spin_unlock(&dentry->d_lock);
 }