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, 29 insertions, 6 deletions

diff --git a/scene/3d/area_3d.cpp b/scene/3d/area_3d.cpp
index fa61ce5546..72f186c676 100644
--- a/scene/3d/area_3d.cpp
+++ b/scene/3d/area_3d.cpp
@@ -230,6 +230,7 @@ void Area3D::_body_inout(int p_status, const RID &p_body, ObjectID p_instance, i
 		return; //likely removed from the tree
 	}
 
+	lock_callback();
 	locked = true;
 
 	if (body_in) {
@@ -279,6 +280,7 @@ void Area3D::_body_inout(int p_status, const RID &p_body, ObjectID p_instance, i
 	}
 
 	locked = false;
+	unlock_callback();
 }
 
 void Area3D::_clear_monitoring() {
@@ -417,6 +419,7 @@ void Area3D::_area_inout(int p_status, const RID &p_area, ObjectID p_instance, i
 		return; //likely removed from the tree
 	}
 
+	lock_callback();
 	locked = true;
 
 	if (area_in) {
@@ -466,6 +469,7 @@ void Area3D::_area_inout(int p_status, const RID &p_area, ObjectID p_instance, i
 	}
 
 	locked = false;
+	unlock_callback();
 }
 
 bool Area3D::is_monitoring() const {
diff --git a/scene/3d/collision_object_3d.cpp b/scene/3d/collision_object_3d.cpp
index c408b0714a..26ada1da5a 100644
--- a/scene/3d/collision_object_3d.cpp
+++ b/scene/3d/collision_object_3d.cpp
@@ -100,10 +100,14 @@ void CollisionObject3D::_notification(int p_what) {
 			bool disabled = !is_enabled();
 
 			if (!disabled || (disable_mode != DISABLE_MODE_REMOVE)) {
-				if (area) {
-					PhysicsServer3D::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 {
-					PhysicsServer3D::get_singleton()->body_set_space(rid, RID());
+					if (area) {
+						PhysicsServer3D::get_singleton()->area_set_space(rid, RID());
+					} else {
+						PhysicsServer3D::get_singleton()->body_set_space(rid, RID());
+					}
 				}
 			}
 
@@ -223,10 +227,14 @@ void CollisionObject3D::_apply_disabled() {
 	switch (disable_mode) {
 		case DISABLE_MODE_REMOVE: {
 			if (is_inside_tree()) {
-				if (area) {
-					PhysicsServer3D::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 {
-					PhysicsServer3D::get_singleton()->body_set_space(rid, RID());
+					if (area) {
+						PhysicsServer3D::get_singleton()->area_set_space(rid, RID());
+					} else {
+						PhysicsServer3D::get_singleton()->body_set_space(rid, RID());
+					}
 				}
 			}
 		} break;
diff --git a/scene/3d/collision_object_3d.h b/scene/3d/collision_object_3d.h
index 656b8c9bf1..ebcbb39e0d 100644
--- a/scene/3d/collision_object_3d.h
+++ b/scene/3d/collision_object_3d.h
@@ -52,6 +52,7 @@ private:
 	bool area = false;
 
 	RID rid;
+	uint32_t callback_lock = 0;
 
 	DisableMode disable_mode = DISABLE_MODE_REMOVE;
 
@@ -97,6 +98,12 @@ private:
 protected:
 	CollisionObject3D(RID p_rid, bool p_area);
 
+	_FORCE_INLINE_ void lock_callback() { callback_lock++; }
+	_FORCE_INLINE_ void unlock_callback() {
+		ERR_FAIL_COND(callback_lock == 0);
+		callback_lock--;
+	}
+
 	void _notification(int p_what);
 	static void _bind_methods();
 
diff --git a/scene/3d/physics_body_3d.cpp b/scene/3d/physics_body_3d.cpp
index 46956b0a2e..106efbc596 100644
--- a/scene/3d/physics_body_3d.cpp
+++ b/scene/3d/physics_body_3d.cpp
@@ -484,6 +484,8 @@ struct _RigidBodyInOut {
 };
 
 void RigidBody3D::_body_state_changed(PhysicsDirectBodyState3D *p_state) {
+	lock_callback();
+
 	set_ignore_transform_notification(true);
 	set_global_transform(p_state->get_transform());
 
@@ -578,6 +580,8 @@ void RigidBody3D::_body_state_changed(PhysicsDirectBodyState3D *p_state) {
 
 		contact_monitor->locked = false;
 	}
+
+	unlock_callback();
 }
 
 void RigidBody3D::_notification(int p_what) {