dcache.c: create helper function for duplicated functionality

This creates a helper function for he "try to ascend into the parent
directory" case, which was written out in triplicate before.  With all
the locking and subtle sequence number stuff, we really don't want to
duplicate that kind of code.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/dcache.c

@@ -1011,6 +1011,34 @@ void shrink_dcache_for_umount(struct super_block *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, int locked, 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 ||
+		 (!locked && read_seqretry(&rename_lock, seq))) {
+		spin_unlock(&new->d_lock);
+		new = NULL;
+	}
+	rcu_read_unlock();
+	return new;
+}
+
+
 /*
  * Search for at least 1 mount point in the dentry's subdirs.
  * We descend to the next level whenever the d_subdirs
@@ -1066,24 +1094,10 @@ int have_submounts(struct dentry *parent)
 	 * All done at this level ... ascend and resume the search.
 	 */
 	if (this_parent != parent) {
-		struct dentry *tmp;
-		struct dentry *child;
-
-		tmp = this_parent->d_parent;
-		rcu_read_lock();
-		spin_unlock(&this_parent->d_lock);
-		child = this_parent;
-		this_parent = tmp;
-		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 ||
-			 (!locked && read_seqretry(&rename_lock, seq))) {
-			spin_unlock(&this_parent->d_lock);
-			rcu_read_unlock();
+		struct dentry *child = this_parent;
+		this_parent = try_to_ascend(this_parent, locked, seq);
+		if (!this_parent)
 			goto rename_retry;
-		}
-		rcu_read_unlock();
 		next = child->d_u.d_child.next;
 		goto resume;
 	}
@@ -1181,24 +1195,10 @@ static int select_parent(struct dentry * parent)
 	 * All done at this level ... ascend and resume the search.
 	 */
 	if (this_parent != parent) {
-		struct dentry *tmp;
-		struct dentry *child;
-
-		tmp = this_parent->d_parent;
-		rcu_read_lock();
-		spin_unlock(&this_parent->d_lock);
-		child = this_parent;
-		this_parent = tmp;
-		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 ||
-			(!locked && read_seqretry(&rename_lock, seq))) {
-			spin_unlock(&this_parent->d_lock);
-			rcu_read_unlock();
+		struct dentry *child = this_parent;
+		this_parent = try_to_ascend(this_parent, locked, seq);
+		if (!this_parent)
 			goto rename_retry;
-		}
-		rcu_read_unlock();
 		next = child->d_u.d_child.next;
 		goto resume;
 	}
@@ -2942,28 +2942,14 @@ void d_genocide(struct dentry *root)
 		spin_unlock(&dentry->d_lock);
 	}
 	if (this_parent != root) {
-		struct dentry *tmp;
-		struct dentry *child;
-
-		tmp = this_parent->d_parent;
+		struct dentry *child = this_parent;
 		if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
 			this_parent->d_flags |= DCACHE_GENOCIDE;
 			this_parent->d_count--;
 		}
-		rcu_read_lock();
-		spin_unlock(&this_parent->d_lock);
-		child = this_parent;
-		this_parent = tmp;
-		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 ||
-			 (!locked && read_seqretry(&rename_lock, seq))) {
-			spin_unlock(&this_parent->d_lock);
-			rcu_read_unlock();
+		this_parent = try_to_ascend(this_parent, locked, seq);
+		if (!this_parent)
 			goto rename_retry;
-		}
-		rcu_read_unlock();
 		next = child->d_u.d_child.next;
 		goto resume;
 	}