ecryptfs: don't leave RCU pathwalk immediately

If the underlying dentry doesn't have ->d_revalidate(), there's no need to
force dropping out of RCU mode.  All we need for that is to make freeing
ecryptfs_dentry_info RCU-delayed.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ecryptfs/dentry.c

@@ -44,15 +44,15 @@
  */
 static int ecryptfs_d_revalidate(struct dentry *dentry, unsigned int flags)
 {
-	struct dentry *lower_dentry;
-	int rc = 1;
+	struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
+	int rc;
+
+	if (!(lower_dentry->d_flags & DCACHE_OP_REVALIDATE))
+		return 1;
 
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
 
-	lower_dentry = ecryptfs_dentry_to_lower(dentry);
-	if (!(lower_dentry->d_flags & DCACHE_OP_REVALIDATE))
-		goto out;
 	rc = lower_dentry->d_op->d_revalidate(lower_dentry, flags);
 	if (dentry->d_inode) {
 		struct inode *lower_inode =
@@ -60,12 +60,17 @@ static int ecryptfs_d_revalidate(struct dentry *dentry, unsigned int flags)
 
 		fsstack_copy_attr_all(dentry->d_inode, lower_inode);
 	}
-out:
 	return rc;
 }
 
 struct kmem_cache *ecryptfs_dentry_info_cache;
 
+static void ecryptfs_dentry_free_rcu(struct rcu_head *head)
+{
+	kmem_cache_free(ecryptfs_dentry_info_cache,
+		container_of(head, struct ecryptfs_dentry_info, rcu));
+}
+
 /**
  * ecryptfs_d_release
  * @dentry: The ecryptfs dentry
@@ -74,15 +79,12 @@ struct kmem_cache *ecryptfs_dentry_info_cache;
  */
 static void ecryptfs_d_release(struct dentry *dentry)
 {
-	if (ecryptfs_dentry_to_private(dentry)) {
-		if (ecryptfs_dentry_to_lower(dentry)) {
-			dput(ecryptfs_dentry_to_lower(dentry));
-			mntput(ecryptfs_dentry_to_lower_mnt(dentry));
-		}
-		kmem_cache_free(ecryptfs_dentry_info_cache,
-				ecryptfs_dentry_to_private(dentry));
+	struct ecryptfs_dentry_info *p = dentry->d_fsdata;
+	if (p) {
+		if (p->lower_path.dentry)
+			path_put(&p->lower_path);
+		call_rcu(&p->rcu, ecryptfs_dentry_free_rcu);
 	}
-	return;
 }
 
 const struct dentry_operations ecryptfs_dops = {

fs/ecryptfs/ecryptfs_kernel.h

@@ -261,7 +261,10 @@ struct ecryptfs_inode_info {
  * vfsmount too. */
 struct ecryptfs_dentry_info {
 	struct path lower_path;
+	union {
 		struct ecryptfs_crypt_stat *crypt_stat;
+		struct rcu_head rcu;
+	};
 };
 
 /**