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[3.14] gh-149156: Fix perf trampoline crash after fork (GH-150347) #150392

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[3.14] gh-149156: Fix perf trampoline crash after fork (GH-150347) #150392

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-05-24-14-45-00.gh-issue-149156.NP73rB.rst
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Original file line number Diff line number Diff line change
@@ -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.
17 changes: 12 additions & 5 deletions Python/perf_trampoline.c
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Original file line number Diff line number Diff line change
Expand Up @@ -211,16 +211,22 @@ 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;
}
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)
{
Expand Down Expand Up @@ -623,9 +629,10 @@ _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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