Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 298094)
+++ channels/chan_sip.c	(working copy)
@@ -12979,7 +12979,16 @@
 {
 	struct sip_pvt *p = data;
 
-	sip_pvt_lock(p);
+	if (sip_pvt_trylock(p)) {
+		/* This can deadlock when handle_statechange is active and we
+		 * also use ast_get_hint with the pvt locked, because lock ordering
+		 * differs, but cannot be changed.
+		 *
+		 * This error return gets handle_statechange to back off and try
+		 * again.
+		 */
+		return -1;
+	}
 
 	switch(state) {
 	case AST_EXTENSION_DEACTIVATED:	/* Retry after a while */
Index: main/pbx.c
===================================================================
--- main/pbx.c	(revision 298094)
+++ main/pbx.c	(working copy)
@@ -3922,12 +3922,30 @@
 
 		/* For general callbacks */
 		AST_LIST_TRAVERSE(&statecbs, cblist, entry) {
-			cblist->callback(hint->exten->parent->name, hint->exten->exten, state, cblist->data);
+			while (cblist->callback(hint->exten->parent->name, hint->exten->exten, state, cblist->data) == -1) {
+				/* -1 means callback failed to get a lock, so unlock everything and retry */
+				ao2_unlock(hint);
+				ao2_unlock(hints);
+				ast_unlock_contexts();
+				sched_yield();
+				ast_rdlock_contexts();
+				ao2_lock(hints);
+				ao2_lock(hint);
+			}
 		}
 
 		/* For extension callbacks */
 		AST_LIST_TRAVERSE(&hint->callbacks, cblist, entry) {
-			cblist->callback(hint->exten->parent->name, hint->exten->exten, state, cblist->data);
+			while (cblist->callback(hint->exten->parent->name, hint->exten->exten, state, cblist->data) == -1) {
+				/* -1 means callback failed to get a lock, so unlock everything and retry */
+				ao2_unlock(hint);
+				ao2_unlock(hints);
+				ast_unlock_contexts();
+				sched_yield();
+				ast_rdlock_contexts();
+				ao2_lock(hints);
+				ao2_lock(hint);
+			}
 		}
 
 		hint->laststate = state;	/* record we saw the change */
@@ -4161,10 +4179,21 @@
 	}
 	ao2_lock(hint);
 
+	if (hint->exten == NULL) {
+		/* the extension has already been destroyed */
+		ao2_unlock(hint);
+		ao2_ref(hint, -1);
+		return 0;
+	}
+
 	while ((cblist = AST_LIST_REMOVE_HEAD(&hint->callbacks, entry))) {
 		/* Notify with -1 and remove all callbacks */
-		cblist->callback(hint->exten->parent->name, hint->exten->exten,
-			AST_EXTENSION_DEACTIVATED, cblist->data);
+		while (cblist->callback(hint->exten->parent->name, hint->exten->exten, AST_EXTENSION_DEACTIVATED, cblist->data) == -1) {
+			/* -1 means callback failed to get a lock, so unlock everything and retry */
+			ast_unlock_contexts();
+			sched_yield();
+			ast_wrlock_contexts(); /* may have only been read locked originally by ast_context_remove_extension_callerid, but others write lock */
+		}
 		ast_free(cblist);
 	}
 
@@ -6776,7 +6805,14 @@
 		if (!exten || !hint) {
 			/* this hint has been removed, notify the watchers */
 			while ((thiscb = AST_LIST_REMOVE_HEAD(&this->callbacks, entry))) {
-				thiscb->callback(this->context, this->exten, AST_EXTENSION_REMOVED, thiscb->data);
+				while (thiscb->callback(this->context, this->exten, AST_EXTENSION_REMOVED, thiscb->data) == -1) {
+					/* -1 means callback failed to get a lock, so unlock everything and retry */
+					ao2_unlock(hints);
+					ast_unlock_contexts();
+					sched_yield();
+					ast_rdlock_contexts();
+					ao2_lock(hints);
+				}
 				ast_free(thiscb);
 			}
 		} else {