--- ../clean/asterisk-1.6.2.16.1/channels/chan_sip.c	2010-12-10 00:10:31.000000000 +0200
+++ channels/chan_sip.c	2011-02-11 12:03:12.000000000 +0200
@@ -7154,14 +7154,18 @@
 
 	sip_pvt_lock(p);
 	fr = sip_rtp_read(ast, p, &faxdetected);
+
+	if (fr == &ast_null_frame) {
+		sip_pvt_unlock(p);
+		return fr;
+	}
+
 	p->lastrtprx = time(NULL);
 
 	/* If we detect a CNG tone and fax detection is enabled then send us off to the fax extension */
 	if (faxdetected && ast_test_flag(&p->flags[1], SIP_PAGE2_FAX_DETECT_CNG)) {
-		ast_channel_lock(ast);
 		if (strcmp(ast->exten, "fax")) {
 			const char *target_context = S_OR(ast->macrocontext, ast->context);
-			ast_channel_unlock(ast);
 			if (ast_exists_extension(ast, target_context, "fax", 1, ast->cid.cid_num)) {
 				ast_verbose(VERBOSE_PREFIX_2 "Redirecting '%s' to fax extension due to CNG detection\n", ast->name);
 				pbx_builtin_setvar_helper(ast, "FAXEXTEN", ast->exten);
@@ -7172,8 +7176,6 @@
 			} else {
 				ast_log(LOG_NOTICE, "FAX CNG detected but no fax extension\n");
                         }
-		} else {
-			ast_channel_unlock(ast);
                 }
         }
 
@@ -22679,14 +22685,10 @@
 		     (t > dialog->lastrtprx + ast_rtp_get_rtpholdtimeout(dialog->rtp)))) {
 			/* Needs a hangup */
 			if (ast_rtp_get_rtptimeout(dialog->rtp)) {
-				while (dialog->owner && ast_channel_trylock(dialog->owner)) {
-					sip_pvt_unlock(dialog);
-					usleep(1);
-					sip_pvt_lock(dialog);
-				}
-				if (!dialog->owner) {
-					return; /* channel hangup can occur during deadlock avoidance. */
-				}
+				/* Don't block the monitor thread.  This function is called often enough
+				 * that we can wait for the next time around. */
+				if ((!dialog->owner) || (dialog->owner && ast_channel_trylock(dialog->owner)))
+					return;
 				ast_log(LOG_NOTICE, "Disconnecting call '%s' for lack of RTP activity in %ld seconds\n",
 					dialog->owner->name, (long) (t - dialog->lastrtprx));
 				/* Issue a softhangup */