Merge pull request #12707 from jmid/domain-assert-failure

Fix assertion race condition in #11800
ocaml · Oct 31, 2023 · 8cc728b · 8cc728b
2 parents d73896d + 2ed291f
commit 8cc728b
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diff --git a/Changes b/Changes
@@ -436,6 +436,9 @@ Working version
 
 ### Bug fixes:
 
+- #11800, #12707: fix an assertion race condition in `install_backup_thread`
+  (Jan Midtgaard, review by Gabriel Scherer)
+
 - #12590, #12595: fix a race in `caml_collect_gc_stats_sample`
   (B. Szilvasy, review by Gabriel Scherer)
 

diff --git a/runtime/domain.c b/runtime/domain.c
@@ -1042,14 +1042,17 @@ static void install_backup_thread (dom_internal* di)
 #endif
 
   if (di->backup_thread_running == 0) {
-    CAMLassert (di->backup_thread_msg == BT_INIT || /* Using fresh domain */
-            di->backup_thread_msg == BT_TERMINATE); /* Reusing domain */
+    uintnat msg;
+    msg = atomic_load_acquire(&di->backup_thread_msg);
+    CAMLassert (msg == BT_INIT || /* Using fresh domain */
+                msg == BT_TERMINATE); /* Reusing domain */
 
-    while (atomic_load_acquire(&di->backup_thread_msg) != BT_INIT) {
+    while (msg != BT_INIT) {
       /* Give a chance for backup thread on this domain to terminate */
       caml_plat_unlock (&di->domain_lock);
       cpu_relax ();
       caml_plat_lock (&di->domain_lock);
+      msg = atomic_load_acquire(&di->backup_thread_msg);
     }
 
 #ifndef _WIN32