AMCL core dumps due to a race condition when used with the map server.

[techtasie]

Bug report

Required Info:

• Operating System:
  • fedora 40
• ROS2 Version: jazzy
  • jazzy
• Version or commit hash: 1.3.1
  • from source: no changes from the source.
• DDS implementation:
  • cyclonedds

Steps to reproduce issue

In the core dump, you see that map_ can be a null pointer and therefore you get an unhandled null pointer exception. Uncommenting those lines circumvented the crash for us:

diff --color -ur navigation2-release-release-jazzy-nav2_amcl-1.3.1-1/src/amcl_node.cpp navigation2-release-release-jazzy-nav2_amcl-1.3.1-1-new/src/amcl_node.cpp
--- navigation2-release-release-jazzy-nav2_amcl-1.3.1-1/src/amcl_node.cpp   2024-06-25 20:01:09.000000000 +0200
+++ navigation2-release-release-jazzy-nav2_amcl-1.3.1-1-new/src/amcl_node.cpp   2024-07-15 17:43:12.792477289 +0200
@@ -540,13 +540,13 @@
       global_frame_id_.c_str());
     return;
   }
-  if (abs(msg->pose.pose.position.x) > map_->size_x ||
-    abs(msg->pose.pose.position.y) > map_->size_y)
-  {
-    RCLCPP_ERROR(
-      get_logger(), "Received initialpose from message is out of the size of map. Rejecting.");
-    return;
-  }
+  // if (abs(msg->pose.pose.position.x) > map_->size_x ||
+  //   abs(msg->pose.pose.position.y) > map_->size_y)
+  // {
+  //   RCLCPP_ERROR(
+  //     get_logger(), "Received initialpose from message is out of the size of map. Rejecting.");
+  //   return;
+  // }

   // Overriding last published pose to initial pose
   last_published_pose_ = *msg;

There is a race condition between the receiving of the map topic subscriber and setting the initial pose. On our robot, this race condition almost always happens but could be hard to reproduce on other setups.

Expected behavior

AMCL localization at initial pose or at least not crashing.

Actual behavior

AMCL coredumps

Additional information

I have attached our core dump. For the core dump, I rebuilt only AMCL in Debug mode; everything else was built as ReleaseWithDebug. core.amcl.1000.c11f12581e0949ccb1dcd9e3d30b45d0.13740.1721053490000000.tar.gz We are using a custom map server that may experience a slight delay when starting up. Therefore, AMCL could be launched without a map.

[SteveMacenski]

That was recently added in https://github.com/ros-navigation/navigation2/pull/4416 by @GoesM during his fuzzing testing.

That makes sense, I think we should check if map_ != nullptr as part of that if statement before dereferencing it. @techtasie can you submit that change and make sure it solves your issue?

i.e.

if (map_ && (abs(msg->pose.pose.position.x) > map_->size_x || abs(msg->pose.pose.position.y) > map_->size_y))

[techtasie]

@SteveMacenski Thank you for your fast reply I will test it thoroughly tomorrow during robocup.

[GoesM]

Oh, so sorry for that! This is entirely caused by my mistake! I didn't notice that this map might be a null pointer.

[techtasie]

Don't we need to still check for the nullptr like this?

  if ( (!first_map_received_) || (map_ && (abs(msg->pose.pose.position.x) > map_->size_x ||
    abs(msg->pose.pose.position.y) > map_->size_y))
  {
    RCLCPP_ERROR(
      get_logger(), "Received initialpose from message is out of the size of map. Rejecting.");
    return;
  }

[techtasie]

I thing the way it is supposed to work is that the initial pose fires directly after the map has been received. Because in some circumstances you want to set the initial pose but get the map a second or so after amcl launch.

[GoesM]

I thing the way it is supposed to work is that the initial pose fires directly after the map has been received. Because in some circumstances you want to set the initial pose but get the map a second or so after amcl launch.

I see. Thanks for your share √ 😀

[SteveMacenski]

I think in that case we just need to check for map_ != nullptr, no? That would have been the behavior prior to the change (i.e. could set the initial pose before a map) so I think that's solid to continue to do

[GoesM]

That would have been the behavior prior to the change

no problem, I misunderstood something before and I've understood it now.

[SteveMacenski]

https://github.com/ros-navigation/navigation2/pull/4605 to resolve. thanks for the note @techtasie !