[Openmp-commits] [PATCH] D125996: [OpenMP][libomp] Fix /dev/shm pollution after forked child process terminates

[Jonathan Peyton via Phabricator via Openmp-commits]

jlpeyton created this revision.
jlpeyton added reviewers: tlwilmar, hbae, AndreyChurbanov.
jlpeyton added a project: OpenMP.
Herald added subscribers: guansong, yaxunl.
Herald added a project: All.
jlpeyton requested review of this revision.
Herald added a reviewer: jdoerfert.
Herald added a subscriber: sstefan1.

Made library registration conditional and skip it in the `__kmp_atfork_child`
handler, postponed it till middle initialization in the child.
This fixes the problem of applications those use e.g. `popen`/`pclose`
which terminate the forked child process.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D125996

Files:
  openmp/runtime/src/kmp.h
  openmp/runtime/src/kmp_global.cpp
  openmp/runtime/src/kmp_runtime.cpp
  openmp/runtime/src/z_Linux_util.cpp


Index: openmp/runtime/src/z_Linux_util.cpp
===================================================================
--- openmp/runtime/src/z_Linux_util.cpp
+++ openmp/runtime/src/z_Linux_util.cpp
@@ -1297,7 +1297,13 @@
   __kmp_itt_reset(); // reset ITT's global state
 #endif /* USE_ITT_BUILD */
 
-  __kmp_serial_initialize();
+  {
+    // Child process often get terminated without any use of OpenMP. That might
+    // cause mapped shared memory file to be left unattended. Thus we postpone
+    // library registration till middle initialization in the child process.
+    __kmp_need_register_serial = FALSE;
+    __kmp_serial_initialize();
+  }
 
   /* This is necessary to make sure no stale data is left around */
   /* AC: customers complain that we use unsafe routines in the atfork
Index: openmp/runtime/src/kmp_runtime.cpp
===================================================================
--- openmp/runtime/src/kmp_runtime.cpp
+++ openmp/runtime/src/kmp_runtime.cpp
@@ -6960,10 +6960,12 @@
   /* Initialize internal memory allocator */
   __kmp_init_allocator();
 
-  /* Register the library startup via an environment variable and check to see
-     whether another copy of the library is already registered. */
-
-  __kmp_register_library_startup();
+  /* Register the library startup via an environment variable or via mapped
+     shared memory file and check to see whether another copy of the library is
+     already registered. Since forked child process is often terminated, we
+     postpone the registration till middle initialization in the child */
+  if (__kmp_need_register_serial)
+    __kmp_register_library_startup();
 
   /* TODO reinitialization of library */
   if (TCR_4(__kmp_global.g.g_done)) {
@@ -7250,6 +7252,12 @@
 
   KA_TRACE(10, ("__kmp_middle_initialize: enter\n"));
 
+  if (UNLIKELY(!__kmp_need_register_serial)) {
+    // We are in a forked child process. The registration was skipped during
+    // serial initialization in __kmp_atfork_child handler. Do it here.
+    __kmp_register_library_startup();
+  }
+
   // Save the previous value for the __kmp_dflt_team_nth so that
   // we can avoid some reinitialization if it hasn't changed.
   prev_dflt_team_nth = __kmp_dflt_team_nth;
Index: openmp/runtime/src/kmp_global.cpp
===================================================================
--- openmp/runtime/src/kmp_global.cpp
+++ openmp/runtime/src/kmp_global.cpp
@@ -44,6 +44,7 @@
 volatile int __kmp_init_serial = FALSE;
 volatile int __kmp_init_gtid = FALSE;
 volatile int __kmp_init_common = FALSE;
+volatile int __kmp_need_register_serial = TRUE;
 volatile int __kmp_init_middle = FALSE;
 volatile int __kmp_init_parallel = FALSE;
 volatile int __kmp_init_hidden_helper = FALSE;
Index: openmp/runtime/src/kmp.h
===================================================================
--- openmp/runtime/src/kmp.h
+++ openmp/runtime/src/kmp.h
@@ -3053,6 +3053,7 @@
 extern volatile int __kmp_init_serial;
 extern volatile int __kmp_init_gtid;
 extern volatile int __kmp_init_common;
+extern volatile int __kmp_need_register_serial;
 extern volatile int __kmp_init_middle;
 extern volatile int __kmp_init_parallel;
 #if KMP_USE_MONITOR


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