Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 129342)
+++ channels/chan_sip.c	(working copy)
@@ -5064,8 +5064,10 @@
 	int fmt;
 	const char *codec;
 
+	ast_channel_lock(p->owner);
 	codec = pbx_builtin_getvar_helper(p->owner, "SIP_CODEC");
-	if (!codec) 
+	if (!codec)
+		ast_channel_unlock(p->owner); 
 		return;
 
 	fmt = ast_getformatbyname(codec);
@@ -5078,6 +5080,7 @@
 			ast_log(LOG_NOTICE, "Ignoring ${SIP_CODEC} variable because it is not shared by both ends.\n");
 	} else
 		ast_log(LOG_NOTICE, "Ignoring ${SIP_CODEC} variable because of unrecognized/not configured codec (check allow/disallow in sip.conf): %s\n", codec);
+	ast_channel_unlock(p->owner);
 	return;	
 }
 
@@ -11383,6 +11386,7 @@
 		referdata->referred_by[0] = '\0';
 	}
 
+	ast_channel_lock(transferer->owner);
 	/* Determine transfer context */
 	if (transferer->owner)	/* Mimic behaviour in res_features.c */
 		transfer_context = pbx_builtin_getvar_helper(transferer->owner, "TRANSFER_CONTEXT");
@@ -11405,7 +11409,9 @@
 	} 
 	if (sip_debug_test_pvt(transferer))
 		ast_verbose("Failed SIP Transfer to non-existing extension %s in context %s\n n", refer_to, transfer_context);
-
+	
+	ast_channel_unlock(transferer->owner);
+	
 	/* Failure, we can't find this extension */
 	return -1;
 }
@@ -11450,6 +11456,7 @@
 	if (sip_debug_test_pvt(p))
 		ast_verbose("Looking for %s in %s\n", c, p->context);
 
+	ast_channel_lock(p->owner);	
 	if (p->owner)	/* Mimic behaviour in res_features.c */
 		transfer_context = pbx_builtin_getvar_helper(p->owner, "TRANSFER_CONTEXT");
 
@@ -11471,7 +11478,7 @@
 	} else if (ast_canmatch_extension(NULL, p->context, c, 1, NULL)) {
 		return 1;
 	}
-
+	ast_channel_unlock(p->owner);
 	return -1;
 }
 
@@ -17449,6 +17456,8 @@
 
 	/* If we are performing an attended transfer and we have two channels involved then copy sound file information to play upon attended transfer completion */
 	if (target.chan2) {
+		ast_channel_lock(target.chan1);
+		ast_channel_lock(target.chan2);
 		const char *chan1_attended_sound = pbx_builtin_getvar_helper(target.chan1, "ATTENDED_TRANSFER_COMPLETE_SOUND"), *chan2_attended_sound = pbx_builtin_getvar_helper(target.chan2, "ATTENDED_TRANSFER_COMPLETE_SOUND");
 		if (!ast_strlen_zero(chan1_attended_sound)) {
 			pbx_builtin_setvar_helper(target.chan1, "BRIDGE_PLAY_SOUND", chan1_attended_sound);
@@ -17456,8 +17465,10 @@
 		if (!ast_strlen_zero(chan2_attended_sound)) {
 			pbx_builtin_setvar_helper(target.chan2, "BRIDGE_PLAY_SOUND", chan2_attended_sound);
 		}
+		ast_channel_lock(target.chan1);
+		ast_channel_lock(target.chan2);
 	}
-
+	
 	/* Perform the transfer */
 	manager_event(EVENT_FLAG_CALL, "Transfer", "TransferMethod: SIP\r\nTransferType: Attended\r\nChannel: %s\r\nUniqueid: %s\r\nSIP-Callid: %s\r\nTargetChannel: %s\r\nTargetUniqueid: %s\r\n",
 		transferer->owner->name,