smack: call WARN_ONCE() instead of calling audit_log_start()

Remove the call to audit_log() (which call audit_log_start()) and deal with
the errors in the caller, logging only once if the condition is met.  Calling
audit_log_start() in this location makes buffer allocation and locking more
complicated in the calling tree (audit_filter_user()).
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

security/smack/smack_lsm.c

@@ -3615,9 +3615,8 @@ static int smack_audit_rule_match(u32 secid, u32 field, u32 op, void *vrule,
 	struct smack_known *skp;
 	char *rule = vrule;
 
-	if (!rule) {
-		audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
-			  "Smack: missing rule\n");
+	if (unlikely(!rule)) {
+		WARN_ONCE(1, "Smack: missing rule\n");
 		return -ENOENT;
 	}