Error when removing a phycics node during a physics callback

* This behavior is not allowed, the error text suggests using call_deferred().
* Added a check in Node::remove_child to prevent future crashes of this type.
* Fixed a performance regression introduced by #36244.

Fixes #63718, probably other crashes too.

4 files changed, 30 insertions, 6 deletions

diff --git a/scene/2d/area_2d.cpp b/scene/2d/area_2d.cpp
index 5eb76bdbb5..f80da6e9ab 100644
--- a/scene/2d/area_2d.cpp
+++ b/scene/2d/area_2d.cpp
@@ -175,6 +175,7 @@ void Area2D::_body_inout(int p_status, const RID &p_body, ObjectID p_instance, i
 		return; //does not exist because it was likely removed from the tree
 	}
 
+	lock_callback();
 	locked = true;
 
 	if (body_in) {
@@ -224,6 +225,7 @@ void Area2D::_body_inout(int p_status, const RID &p_body, ObjectID p_instance, i
 	}
 
 	locked = false;
+	unlock_callback();
 }
 
 void Area2D::_area_enter_tree(ObjectID p_id) {
@@ -268,6 +270,8 @@ void Area2D::_area_inout(int p_status, const RID &p_area, ObjectID p_instance, i
 	if (!area_in && !E) {
 		return; //likely removed from the tree
 	}
+
+	lock_callback();
 	locked = true;
 
 	if (area_in) {
@@ -317,6 +321,7 @@ void Area2D::_area_inout(int p_status, const RID &p_area, ObjectID p_instance, i
 	}
 
 	locked = false;
+	unlock_callback();
 }
 
 void Area2D::_clear_monitoring() {
diff --git a/scene/2d/collision_object_2d.cpp b/scene/2d/collision_object_2d.cpp
index b2fee6ad82..caea753d99 100644
--- a/scene/2d/collision_object_2d.cpp
+++ b/scene/2d/collision_object_2d.cpp
@@ -94,10 +94,14 @@ void CollisionObject2D::_notification(int p_what) {
 			bool disabled = !is_enabled();
 
 			if (!disabled || (disable_mode != DISABLE_MODE_REMOVE)) {
-				if (area) {
-					PhysicsServer2D::get_singleton()->area_set_space(rid, RID());
+				if (callback_lock > 0) {
+					ERR_PRINT("Removing a CollisionObject node during a physics callback is not allowed and will cause undesired behavior. Remove with call_deferred() instead.");
 				} else {
-					PhysicsServer2D::get_singleton()->body_set_space(rid, RID());
+					if (area) {
+						PhysicsServer2D::get_singleton()->area_set_space(rid, RID());
+					} else {
+						PhysicsServer2D::get_singleton()->body_set_space(rid, RID());
+					}
 				}
 			}
 
@@ -225,10 +229,14 @@ void CollisionObject2D::_apply_disabled() {
 	switch (disable_mode) {
 		case DISABLE_MODE_REMOVE: {
 			if (is_inside_tree()) {
-				if (area) {
-					PhysicsServer2D::get_singleton()->area_set_space(rid, RID());
+				if (callback_lock > 0) {
+					ERR_PRINT("Disabling a CollisionObject node during a physics callback is not allowed and will cause undesired behavior. Disable with call_deferred() instead.");
 				} else {
-					PhysicsServer2D::get_singleton()->body_set_space(rid, RID());
+					if (area) {
+						PhysicsServer2D::get_singleton()->area_set_space(rid, RID());
+					} else {
+						PhysicsServer2D::get_singleton()->body_set_space(rid, RID());
+					}
 				}
 			}
 		} break;
diff --git a/scene/2d/collision_object_2d.h b/scene/2d/collision_object_2d.h
index d44e402e96..88429b145d 100644
--- a/scene/2d/collision_object_2d.h
+++ b/scene/2d/collision_object_2d.h
@@ -53,6 +53,7 @@ private:
 
 	bool area = false;
 	RID rid;
+	uint32_t callback_lock = 0;
 	bool pickable = false;
 
 	DisableMode disable_mode = DISABLE_MODE_REMOVE;
@@ -83,6 +84,12 @@ private:
 	void _apply_enabled();
 
 protected:
+	_FORCE_INLINE_ void lock_callback() { callback_lock++; }
+	_FORCE_INLINE_ void unlock_callback() {
+		ERR_FAIL_COND(callback_lock == 0);
+		callback_lock--;
+	}
+
 	CollisionObject2D(RID p_rid, bool p_area);
 
 	void _notification(int p_what);
diff --git a/scene/2d/physics_body_2d.cpp b/scene/2d/physics_body_2d.cpp
index 9fee99c6a7..1721bcde3b 100644
--- a/scene/2d/physics_body_2d.cpp
+++ b/scene/2d/physics_body_2d.cpp
@@ -434,6 +434,8 @@ struct _RigidBody2DInOut {
 };
 
 void RigidBody2D::_body_state_changed(PhysicsDirectBodyState2D *p_state) {
+	lock_callback();
+
 	set_block_transform_notify(true); // don't want notify (would feedback loop)
 	if (!freeze || freeze_mode != FREEZE_MODE_KINEMATIC) {
 		set_global_transform(p_state->get_transform());
@@ -527,6 +529,8 @@ void RigidBody2D::_body_state_changed(PhysicsDirectBodyState2D *p_state) {
 
 		contact_monitor->locked = false;
 	}
+
+	unlock_callback();
 }
 
 void RigidBody2D::_apply_body_mode() {