don't remove DLX when not found

The warnings now looks like this:

=WARNING REPORT==== 24-Feb-2012::17:06:55 ===
Dead-letter-exchange <<"dead.letter.exchange">> for queue
<<"test.queue.dead.letter">> does not exist.  Disabling DLX for this queue.

=WARNING REPORT==== 24-Feb-2012::17:06:55 ===
Dead-letter-exchange <<"dead.letter.exchange">> for queue
<<"test.queue.dead.letter">> is back.  DLX works again for this queue.

Again, only the first message causes a warning.

1 files changed, 27 insertions, 11 deletions

diff --git a/src/rabbit_amqqueue_process.erl b/src/rabbit_amqqueue_process.erl
index dcd6ae08ba..9c5510cb49 100644
--- a/src/rabbit_amqqueue_process.erl
+++ b/src/rabbit_amqqueue_process.erl
@@ -56,7 +56,8 @@
             delayed_stop,
             queue_monitors,
             dlx,
-            dlx_routing_key
+            dlx_routing_key,
+            dlx_failed
            }).
 
 -record(consumer, {tag, ack_required}).
@@ -137,6 +138,7 @@ init(Q) ->
                ttl                 = undefined,
                dlx                 = undefined,
                dlx_routing_key     = undefined,
+               dlx_failed          = false,
                publish_seqno       = 1,
                unconfirmed_mq      = gb_trees:empty(),
                unconfirmed_qm      = gb_trees:empty(),
@@ -733,21 +735,35 @@ dead_letter_fun(Reason, _State) ->
             gen_server2:cast(self(), {dead_letter, {Msg, AckTag}, Reason})
     end.
 
-dead_letter_msg(Msg, AckTag, Reason, State = #q{dlx = undefined}) ->
+dead_letter_exchange_missing_warn(Status, Status, _DLX, _State) ->
+    ok;
+dead_letter_exchange_missing_warn(_Status, Failed, DLX, State) ->
+    #resource{name = QName} = qname(State),
+    #resource{name = XName} = DLX,
+    case Failed of
+        true ->
+            rabbit_log:warning("Dead-letter-exchange ~p for queue " ++
+                               "~p does not exist.  Disabling DLX " ++
+                               "for this queue.~n", [XName, QName]);
+        false ->
+            rabbit_log:warning("Dead-letter-exchange ~p for queue " ++
+                               "~p is back.  DLX works again " ++
+                               "for this queue.~n", [XName, QName])
+    end.
+
+dead_letter_msg(_Msg, _AckTag, _Reason, State = #q{dlx = undefined}) ->
     %% Dead-lettring already disabled for this queue.
     noreply(State);
-dead_letter_msg(Msg, AckTag, Reason, State = #q{dlx = DLX}) ->
+dead_letter_msg(Msg, AckTag, Reason, State = #q{dlx        = DLX,
+                                                dlx_failed = Status}) ->
     case rabbit_exchange:lookup(DLX) of
         {error, not_found} ->
-            #resource{name = QName} = qname(State),
-            #resource{name = XName} = DLX,
-            rabbit_log:warning("Dead-letter-exchange ~p for queue ~p does " ++
-                               "not exist.  Disabling DLX for this queue.~n",
-                               [XName, QName]),
-            noreply(State#q{dlx             = undefined,
-                            dlx_routing_key = undefined});
+            dead_letter_exchange_missing_warn(Status, true, DLX, State),
+            noreply(State#q{dlx_failed = true});
         _ ->
-            dead_letter_msg_existing_dlx(Msg, AckTag, Reason, State)
+            dead_letter_exchange_missing_warn(Status, false, DLX, State),
+            dead_letter_msg_existing_dlx(Msg, AckTag, Reason,
+                                         State#q{dlx_failed = false})
     end.
 
 dead_letter_msg_existing_dlx(Msg, AckTag, Reason,