[Bug]: CHPL_TASKS=fifo + CHPL_COMM=gasnet segfaults in runtime startup

[jabraham17]

Running hello world with CHPL_TASKS=fifo + CHPL_COMM=gasnet segfaults during runtime startup. Using GASNET_BACKTRACE=1, I traced this to a failure in partitionResources, because topology is NULL.

I believe this is because partitionResources is called when it should not be. Making the following to chpl_topo_post_comm_init (to match other chpl_topo_ functions) partially fixes the issue

diff --git a/runtime/src/topo/hwloc/topo-hwloc.c b/runtime/src/topo/hwloc/topo-hwloc.c
index f6188ea24ed..0ae99532b0a 100644
--- a/runtime/src/topo/hwloc/topo-hwloc.c
+++ b/runtime/src/topo/hwloc/topo-hwloc.c
@@ -242,6 +242,9 @@ void chpl_topo_pre_comm_init(char *accessiblePUsMask) {
 // initialized.
 //
 void chpl_topo_post_comm_init(void) {
+  if (!haveTopology) {
+    return;
+  }
   partitionResources();
 }
 

After making this change, hello world exists with "error: number of cpus is uninitialized". So something needs to be done to properly initialize the number of cpus

One way this can be done is by changing chpl_topo_pre_comm_init to make sure it initializes the topology when using tasks=fifo, but this feels heavy handed (based on code comments).

I think this is only an issue when CHPL_HWLOC is not explicitly set, as it defaults to CHPL_HWLOC=none when CHPL_TASKS!=qthreads. And with CHPL_HWLOC=none, this code is not used.

chplenv

CHPL_HOST_PLATFORM: darwin
CHPL_HOST_COMPILER: clang
  CHPL_HOST_CC: clang
  CHPL_HOST_CXX: clang++
CHPL_HOST_ARCH: arm64
CHPL_TARGET_PLATFORM: darwin
CHPL_TARGET_COMPILER: clang *
  CHPL_TARGET_CC: clang
  CHPL_TARGET_CXX: clang++
  CHPL_TARGET_LD: /usr/bin/clang++
CHPL_TARGET_ARCH: arm64
CHPL_TARGET_CPU: native *
CHPL_LOCALE_MODEL: flat
CHPL_COMM: gasnet *
  CHPL_COMM_SUBSTRATE: udp
  CHPL_GASNET_SEGMENT: everything
CHPL_TASKS: fifo *
CHPL_LAUNCHER: amudprun
CHPL_TIMERS: generic
CHPL_UNWIND: none
CHPL_HOST_MEM: cstdlib
CHPL_MEM: cstdlib *
CHPL_ATOMICS: cstdlib
  CHPL_NETWORK_ATOMICS: none
CHPL_GMP: system *
CHPL_HWLOC: system *
CHPL_RE2: bundled *
CHPL_LLVM: system
  CHPL_LLVM_SUPPORT: system
  CHPL_LLVM_CONFIG: /opt/homebrew/opt/llvm@19/bin/llvm-config
  CHPL_LLVM_VERSION: 19
CHPL_AUX_FILESYS: none
CHPL_LIB_PIC: none
CHPL_SANITIZE: none
CHPL_SANITIZE_EXE: none

[jabraham17]

I discussed this offline with @jhh67, we determined that the correct thing to do is the "heavy handed" approach and just make sure to initialize topology when CHPL_TASKS=fifo. This led to removing haveTopology entirely, as now the check for CHPL_TASKS is whether it is fifo or qthreads, which will always be true.

#26415 will do that and resolve this issue.