GFS2: Post-VFS scale update for RCU path walk

We can allow a few more cases to use RCU path walking than
originally allowed. It should be possible to also enable
RCU path walking when the glock is already cached. Thats
a bit more complicated though, so left for a future patch.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Nick Piggin <npiggin@gmail.com>

fs/gfs2/acl.c

@@ -80,8 +80,11 @@ int gfs2_check_acl(struct inode *inode, int mask, unsigned int flags)
 	struct posix_acl *acl;
 	int error;
 
-	if (flags & IPERM_FLAG_RCU)
-		return -ECHILD;
+	if (flags & IPERM_FLAG_RCU) {
+		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
+			return -ECHILD;
+		return -EAGAIN;
+	}
 
 	acl = gfs2_acl_get(GFS2_I(inode), ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))