NFS: Also use readdir info to revalidate positive dentries

If the fileid of the cached dentry fails to match that returned by
the readdir call, then we should also d_drop. Try to take into account the
fact that on NFSv4, readdir may return the "mounted_on_fileid" by looking
for submounts.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -1124,9 +1124,16 @@ static struct dentry *nfs_readdir_lookup(nfs_readdir_descriptor_t *desc)
 	name.hash = full_name_hash(name.name, name.len);
 	dentry = d_lookup(parent, &name);
 	if (dentry != NULL) {
-		/* Is this a positive dentry? */
-		if (dentry->d_inode != NULL)
-			return dentry;
+		/* Is this a positive dentry that matches the readdir info? */
+		if (dentry->d_inode != NULL &&
+				(NFS_FILEID(dentry->d_inode) == entry->ino ||
+				d_mountpoint(dentry))) {
+			if (!desc->plus || entry->fh->size == 0)
+				return dentry;
+			if (nfs_compare_fh(NFS_FH(dentry->d_inode),
+						entry->fh) == 0)
+				goto out_renew;
+		}
 		/* No, so d_drop to allow one to be created */
 		d_drop(dentry);
 		dput(dentry);
@@ -1152,6 +1159,7 @@ static struct dentry *nfs_readdir_lookup(nfs_readdir_descriptor_t *desc)
 		dentry = alias;
 	}
 
+out_renew:
 	nfs_renew_times(dentry);
 	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
 	return dentry;