https://github.com/python/cpython/commit/9989a54a5333a4ce8d7893d3468d8187e6e3b13b
commit: 9989a54a5333a4ce8d7893d3468d8187e6e3b13b
branch: main
author: Pablo Galindo Salgado <[email protected]>
committer: pablogsal <[email protected]>
date: 2026-05-25T13:45:58+01:00
summary:
gh-149156: Fix perf trampoline crash after fork (#150347)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-05-24-14-45-00.gh-issue-149156.NP73rB.rst
M Python/perf_trampoline.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-05-24-14-45-00.gh-issue-149156.NP73rB.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-24-14-45-00.gh-issue-149156.NP73rB.rst
new file mode 100644
index 00000000000000..2cb091e2b162f6
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-24-14-45-00.gh-issue-149156.NP73rB.rst
@@ -0,0 +1,3 @@
+Fix an intermittent crash after :func:`os.fork` when perf trampoline
+profiling is enabled and the child returns through trampoline frames
+inherited from the parent process.
diff --git a/Python/perf_trampoline.c b/Python/perf_trampoline.c
index 58c61e64bfc4e9..d90b789c2b5712 100644
--- a/Python/perf_trampoline.c
+++ b/Python/perf_trampoline.c
@@ -210,9 +210,8 @@ enum perf_trampoline_type {
static void free_code_arenas(void);
static void
-perf_trampoline_reset_state(void)
+perf_trampoline_clear_code_watcher(void)
{
- free_code_arenas();
if (code_watcher_id >= 0) {
PyCode_ClearWatcher(code_watcher_id);
code_watcher_id = -1;
@@ -220,6 +219,13 @@ perf_trampoline_reset_state(void)
extra_code_index = -1;
}
+static void
+perf_trampoline_reset_state(void)
+{
+ free_code_arenas();
+ perf_trampoline_clear_code_watcher();
+}
+
static int
perf_trampoline_code_watcher(PyCodeEvent event, PyCodeObject *co)
{
@@ -621,9 +627,10 @@ _PyPerfTrampoline_AfterFork_Child(void)
// After fork, Fini may leave the old code watcher registered
// if trampolined code objects from the parent still exist
// (trampoline_refcount > 0). Clear it unconditionally before
- // Init registers a new one, to prevent two watchers sharing
- // the same globals and double-decrementing trampoline_refcount.
- perf_trampoline_reset_state();
+ // Init registers a new one, but keep the old arenas mapped: the
+ // child may still need to return through trampoline frames that
+ // were on the C stack at fork().
+ perf_trampoline_clear_code_watcher();
_PyPerfTrampoline_Init(1);
}
}
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