Index: asterisk-1.6.2.18/channels/chan_sip.c
===================================================================
--- asterisk-1.6.2.18.orig/channels/chan_sip.c	2011-05-19 14:30:23.000000000 +0100
+++ asterisk-1.6.2.18/channels/chan_sip.c	2011-05-19 14:31:31.000000000 +0100
@@ -22738,6 +22738,12 @@
 			}
 		}
 		ast_free(req);
+		if (p->owner && nounlock) {
+			/* We have an owner channel, which has been unlocked for some reason, so our pre-requisite
+			 * for running handle_incoming() is no-longer met... Bail now.
+			 */
+			break;
+		}
 	}
 }
 
@@ -22747,6 +22753,7 @@
 	int recount = 0;
 	int nounlock = 0;
 	int lockretry;
+	int retry;
 
 	for (lockretry = 10; lockretry > 0; lockretry--) {
 		sip_pvt_lock(p);
@@ -22765,7 +22772,7 @@
 	}
 
 	if (!lockretry) {
-		int retry = !AST_LIST_EMPTY(&p->request_queue);
+		retry = !AST_LIST_EMPTY(&p->request_queue);
 
 		/* we couldn't get the owner lock, which is needed to process
 		   the queued requests, so return a non-zero value, which will
@@ -22780,8 +22787,12 @@
 	};
 
 	process_request_queue(p, &recount, &nounlock);
-	p->request_queue_sched_id = -1;
 
+	/* If one of the inbound packets caused a channel unlock, then we may not fully drain the queue */
+	retry = !AST_LIST_EMPTY(&p->request_queue);
+	if (!retry) {
+		p->request_queue_sched_id = -1;
+	}
 	if (p->owner && !nounlock) {
 		ast_channel_unlock(p->owner);
 	}
@@ -22791,9 +22802,10 @@
 		ast_update_use_count();
 	}
 
-	dialog_unref(p, "The ref to a dialog passed to this sched callback is going out of scope; unref it.");
-
-	return 0;
+	if (!retry) {
+		dialog_unref(p, "The ref to a dialog passed to this sched callback is going out of scope; unref it.");
+	}
+	return retry;
 }
 
 static int queue_request(struct sip_pvt *p, const struct sip_request *req)
@@ -22964,8 +22976,22 @@
 		AST_SCHED_DEL_UNREF(sched, p->request_queue_sched_id, dialog_unref(p, "when you delete the request_queue_sched_id sched, you should dec the refcount for the stored dialog ptr"));
 		process_request_queue(p, &recount, &nounlock);
 	}
-
-	if (handle_incoming(p, req, sin, &recount, &nounlock) == -1) {
+	if( !AST_LIST_EMPTY(&p->request_queue) || (p->owner && nounlock) ) {
+		/* Our p->owner is not locked for some reason, or we could not flush the queue
+		 * Queue the packet we just received for later */
+                if (queue_request(p, req)) {
+                        /* the queue request has failed! */
+			ast_log(LOG_ERROR, "Channel %s became unlocked, and request was unable to be queued.\n", S_OR(p->owner->name, "- no channel name ??? - "));
+			ast_log(LOG_ERROR, "SIP transaction failed: %s \n", p->callid);
+			if (req->method != SIP_ACK)
+				transmit_response(p, "503 Server error", req);  /* We must respond according to RFC 3261 sec 12.2 */
+
+			/* If the queue still has entries, try to reschedule */
+			if (!AST_LIST_EMPTY(&p->request_queue) && (p->request_queue_sched_id = ast_sched_add(sched, 10, scheduler_process_request_queue, dialog_ref(p, "Increment refcount to pass dialog pointer to sched callback"))) == -1) {
+				dialog_unref(p, "Decrement refcount due to sched_add failure");
+			}
+                }
+	} else if (handle_incoming(p, req, sin, &recount, &nounlock) == -1) {
 		/* Request failed */
 		ast_debug(1, "SIP message could not be handled, bad request: %-70.70s\n", p->callid[0] ? p->callid : "<no callid>");
 	}