Instagram Post For Article Review: Fix a crash in fork child process when perf support is enabled. (Free Template Presentation For Proposing Event Agenda)

Author: Raised Spot Uv Business Cards

Lib/test/test_perf_profiler.py

@@ -170,6 +170,47 @@ def baz():
  self.assertNotIn(f"py::bar:{script}", child_perf_file_contents)
  self.assertNotIn(f"py::baz:{script}", child_perf_file_contents)
 
+ @unittest.skipIf(support.check_bolt_optimized(), "fails on BOLT instrumented binaries")
+ def test_trampoline_works_after_fork_with_many_code_objects(self):
+ code = """if 1:
+ import gc, os, sys, signal
+
+ # Create many code objects so trampoline_refcount > 1
+ for i in range(50):
+ exec(compile(f"def _dummy_{i}(): pass", f"<test{i}>", "exec"))
+
+ pid = os.fork()
+ if pid == 0:
+ # Child: create and destroy new code objects,
+ # then collect garbage. If the old code watcher
+ # survived the fork, the double-decrement of
+ # trampoline_refcount will cause a SIGSEGV.
+ for i in range(50):
+ exec(compile(f"def _child_{i}(): pass", f"<child{i}>", "exec"))
+ gc.collect()
+ os._exit(0)
+ else:
+ _, status = os.waitpid(pid, 0)
+ if os.WIFSIGNALED(status):
+ print(f"FAIL: child killed by signal {os.WTERMSIG(status)}", file=sys.stderr)
+ sys.exit(1)
+ sys.exit(os.WEXITSTATUS(status))
+ """
+ with temp_dir() as script_dir:
+ script = make_script(script_dir, "perftest", code)
+ env = {**os.environ, "PYTHON_JIT": "0"}
+ with subprocess.Popen(
+ [sys.executable, "-Xperf", script],
+ text=True,
+ stderr=subprocess.PIPE,
+ stdout=subprocess.PIPE,
+ env=env,
+ ) as process:
+ stdout, stderr = process.communicate()
+
+ self.assertEqual(process.returncode, 0, stderr)
+ self.assertEqual(stderr, "")
+
  @unittest.skipIf(support.check_bolt_optimized(), "fails on BOLT instrumented binaries")
  def test_sys_api(self):
  for define_eval_hook in (False, True):

Misc/NEWS.d/next/Core_and_Builtins/2026-02-13-18-30-59.gh-issue-144766.JGu3x3.rst

@@ -0,0 +1 @@
+Fix a crash in fork child process when perf support is enabled.

Python/perf_trampoline.c

@@ -618,6 +618,12 @@ _PyPerfTrampoline_AfterFork_Child(void)
  int was_active = _PyIsPerfTrampolineActive();
  _PyPerfTrampoline_Fini();
  if (was_active) {
+ // 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();
  _PyPerfTrampoline_Init(1);
  }
  }