fold try_to_ascend() into the sole remaining caller

There used to be a bunch of tree-walkers in dcache.c, all alike.
try_to_ascend() had been introduced to abstract a piece of logics
duplicated in all of them.  These days all these tree-walkers are
implemented via the same iterator (d_walk()), which is the only
remaining caller of try_to_ascend(), so let's fold it back...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -438,7 +438,7 @@ static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
 {
 	list_del(&dentry->d_u.d_child);
 	/*
-	 * Inform try_to_ascend() that we are no longer attached to the
+	 * Inform d_walk() that we are no longer attached to the
 	 * dentry tree
 	 */
 	dentry->d_flags |= DCACHE_DENTRY_KILLED;
@@ -1038,34 +1038,6 @@ void shrink_dcache_sb(struct super_block *sb)
 }
 EXPORT_SYMBOL(shrink_dcache_sb);
 
-/*
- * This tries to ascend one level of parenthood, but
- * we can race with renaming, so we need to re-check
- * the parenthood after dropping the lock and check
- * that the sequence number still matches.
- */
-static struct dentry *try_to_ascend(struct dentry *old, unsigned seq)
-{
-	struct dentry *new = old->d_parent;
-
-	rcu_read_lock();
-	spin_unlock(&old->d_lock);
-	spin_lock(&new->d_lock);
-
-	/*
-	 * might go back up the wrong parent if we have had a rename
-	 * or deletion
-	 */
-	if (new != old->d_parent ||
-		 (old->d_flags & DCACHE_DENTRY_KILLED) ||
-		 need_seqretry(&rename_lock, seq)) {
-		spin_unlock(&new->d_lock);
-		new = NULL;
-	}
-	rcu_read_unlock();
-	return new;
-}
-
 /**
  * enum d_walk_ret - action to talke during tree walk
  * @D_WALK_CONTINUE:	contrinue walk
@@ -1154,9 +1126,24 @@ static void d_walk(struct dentry *parent, void *data,
 	 */
 	if (this_parent != parent) {
 		struct dentry *child = this_parent;
-		this_parent = try_to_ascend(this_parent, seq);
-		if (!this_parent)
+		this_parent = child->d_parent;
+
+		rcu_read_lock();
+		spin_unlock(&child->d_lock);
+		spin_lock(&this_parent->d_lock);
+
+		/*
+		 * might go back up the wrong parent if we have had a rename
+		 * or deletion
+		 */
+		if (this_parent != child->d_parent ||
+			 (child->d_flags & DCACHE_DENTRY_KILLED) ||
+			 need_seqretry(&rename_lock, seq)) {
+			spin_unlock(&this_parent->d_lock);
+			rcu_read_unlock();
 			goto rename_retry;
+		}
+		rcu_read_unlock();
 		next = child->d_u.d_child.next;
 		goto resume;
 	}