nfs{,4}_lookup_validate(): use stable parent inode passed by caller

we can't kill __nfs_lookup_revalidate() completely, but ->d_parent boilerplate
in it is gone

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nfs/dir.c

@@ -1732,8 +1732,8 @@ static int nfs_lookup_revalidate_dentry(struct inode *dir,
  * cached dentry and do a new lookup.
  */
 static int
-nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
-			 unsigned int flags)
+nfs_do_lookup_revalidate(struct inode *dir, const struct qstr *name,
+			 struct dentry *dentry, unsigned int flags)
 {
 	struct inode *inode;
 	int error = 0;
@@ -1785,39 +1785,26 @@ nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 }
 
 static int
-__nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags,
-			int (*reval)(struct inode *, struct dentry *, unsigned int))
+__nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
 {
-	struct dentry *parent;
-	struct inode *dir;
-	int ret;
-
 	if (flags & LOOKUP_RCU) {
 		if (dentry->d_fsdata == NFS_FSDATA_BLOCKED)
 			return -ECHILD;
-		parent = READ_ONCE(dentry->d_parent);
-		dir = d_inode_rcu(parent);
-		if (!dir)
-			return -ECHILD;
-		ret = reval(dir, dentry, flags);
-		if (parent != READ_ONCE(dentry->d_parent))
-			return -ECHILD;
 	} else {
 		/* Wait for unlink to complete - see unblock_revalidate() */
 		wait_var_event(&dentry->d_fsdata,
 			       smp_load_acquire(&dentry->d_fsdata)
 			       != NFS_FSDATA_BLOCKED);
-		parent = dget_parent(dentry);
-		ret = reval(d_inode(parent), dentry, flags);
-		dput(parent);
 	}
-	return ret;
+	return 0;
 }
 
 static int nfs_lookup_revalidate(struct inode *dir, const struct qstr *name,
 				 struct dentry *dentry, unsigned int flags)
 {
-	return __nfs_lookup_revalidate(dentry, flags, nfs_do_lookup_revalidate);
+	if (__nfs_lookup_revalidate(dentry, flags))
+		return -ECHILD;
+	return nfs_do_lookup_revalidate(dir, name, dentry, flags);
 }
 
 static void block_revalidate(struct dentry *dentry)
@@ -2216,11 +2203,14 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 EXPORT_SYMBOL_GPL(nfs_atomic_open);
 
 static int
-nfs4_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
-			  unsigned int flags)
+nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
+		       struct dentry *dentry, unsigned int flags)
 {
 	struct inode *inode;
 
+	if (__nfs_lookup_revalidate(dentry, flags))
+		return -ECHILD;
+
 	trace_nfs_lookup_revalidate_enter(dir, dentry, flags);
 
 	if (!(flags & LOOKUP_OPEN) || (flags & LOOKUP_DIRECTORY))
@@ -2259,14 +2249,7 @@ nfs4_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 	return nfs_lookup_revalidate_dentry(dir, dentry, inode, flags);
 
 full_reval:
-	return nfs_do_lookup_revalidate(dir, dentry, flags);
-}
-
-static int nfs4_lookup_revalidate(struct inode *dir, const struct qstr *name,
-				  struct dentry *dentry, unsigned int flags)
-{
-	return __nfs_lookup_revalidate(dentry, flags,
-			nfs4_do_lookup_revalidate);
+	return nfs_do_lookup_revalidate(dir, name, dentry, flags);
 }
 
 #endif /* CONFIG_NFSV4 */