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Merged
colesbury merged 3 commits into from
Mar 21, 2024
Merged

gh-116522: Stop the world before fork() and during shutdown #116607

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c2ebedb
gh-116522: Stop the world before fork() and during shutdown
colesbury Mar 8, 2024
b13d1e5
Move stop-the-world call before setting finalized
colesbury Mar 12, 2024
4772a69
Add comment and assertion to warn_about_fork_with_threads
colesbury Mar 20, 2024
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28 changes: 21 additions & 7 deletions Modules/posixmodule.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -613,11 +613,16 @@ PyOS_BeforeFork(void)
run_at_forkers(interp->before_forkers, 1);

_PyImport_AcquireLock(interp);
_PyEval_StopTheWorldAll(&_PyRuntime);
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HEAD_LOCK(&_PyRuntime);
}

void
PyOS_AfterFork_Parent(void)
{
HEAD_UNLOCK(&_PyRuntime);
_PyEval_StartTheWorldAll(&_PyRuntime);

PyInterpreterState *interp = _PyInterpreterState_GET();
if (_PyImport_ReleaseLock(interp) <= 0) {
Py_FatalError("failed releasing import lock after fork");
Expand All@@ -632,6 +637,7 @@ PyOS_AfterFork_Child(void)
PyStatus status;
_PyRuntimeState *runtime = &_PyRuntime;

// re-creates runtime->interpreters.mutex (HEAD_UNLOCK)
status = _PyRuntimeState_ReInitThreads(runtime);
if (_PyStatus_EXCEPTION(status)) {
goto fatal_error;
Expand DownExpand Up@@ -7731,10 +7737,15 @@ os_register_at_fork_impl(PyObject *module, PyObject *before,
// running in the process. Best effort, silent if unable to count threads.
// Constraint: Quick. Never overcounts. Never leaves an error set.
//
// This code might do an import, thus acquiring the import lock, which
// PyOS_BeforeFork() also does. As this should only be called from
// the parent process, it is in the same thread so that works.
static void warn_about_fork_with_threads(const char* name) {
// This should only be called from the parent process after
// PyOS_AfterFork_Parent().
static void
warn_about_fork_with_threads(const char* name)
{
// It's not safe to issue the warning while the world is stopped, because
// other threads might be holding locks that we need, which would deadlock.
assert(!_PyRuntime.stoptheworld.world_stopped);

// TODO: Consider making an `os` module API to return the current number
// of threads in the process. That'd presumably use this platform code but
// raise an error rather than using the inaccurate fallback.
Expand DownExpand Up@@ -7858,9 +7869,10 @@ os_fork1_impl(PyObject *module)
/* child: this clobbers and resets the import lock. */
PyOS_AfterFork_Child();
} else {
warn_about_fork_with_threads("fork1");
/* parent: release the import lock. */
PyOS_AfterFork_Parent();
// After PyOS_AfterFork_Parent() starts the world to avoid deadlock.
warn_about_fork_with_threads("fork1");
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}
if (pid == -1) {
errno = saved_errno;
Expand DownExpand Up@@ -7906,9 +7918,10 @@ os_fork_impl(PyObject *module)
/* child: this clobbers and resets the import lock. */
PyOS_AfterFork_Child();
} else {
warn_about_fork_with_threads("fork");
/* parent: release the import lock. */
PyOS_AfterFork_Parent();
// After PyOS_AfterFork_Parent() starts the world to avoid deadlock.
warn_about_fork_with_threads("fork");
}
if (pid == -1) {
errno = saved_errno;
Expand DownExpand Up@@ -8737,9 +8750,10 @@ os_forkpty_impl(PyObject *module)
/* child: this clobbers and resets the import lock. */
PyOS_AfterFork_Child();
} else {
warn_about_fork_with_threads("forkpty");
/* parent: release the import lock. */
PyOS_AfterFork_Parent();
// After PyOS_AfterFork_Parent() starts the world to avoid deadlock.
warn_about_fork_with_threads("forkpty");
}
if (pid == -1) {
return posix_error();
Expand Down
3 changes: 3 additions & 0 deletions Python/pylifecycle.c
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Expand Up@@ -1911,6 +1911,9 @@ Py_FinalizeEx(void)
int malloc_stats = tstate->interp->config.malloc_stats;
#endif

/* Ensure that remaining threads are detached */
_PyEval_StopTheWorldAll(runtime);
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/* Remaining daemon threads will automatically exit
when they attempt to take the GIL (ex: PyEval_RestoreThread()). */
_PyInterpreterState_SetFinalizing(tstate->interp, tstate);
Expand Down
6 changes: 6 additions & 0 deletions Python/pystate.c
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Expand Up@@ -1715,6 +1715,10 @@ _PyThreadState_DeleteExcept(PyThreadState *tstate)
PyInterpreterState *interp = tstate->interp;
_PyRuntimeState *runtime = interp->runtime;

#ifdef Py_GIL_DISABLED
assert(runtime->stoptheworld.world_stopped);
#endif

HEAD_LOCK(runtime);
/* Remove all thread states, except tstate, from the linked list of
thread states. This will allow calling PyThreadState_Clear()
Expand All@@ -1733,6 +1737,8 @@ _PyThreadState_DeleteExcept(PyThreadState *tstate)
interp->threads.head = tstate;
HEAD_UNLOCK(runtime);

_PyEval_StartTheWorldAll(runtime);

/* Clear and deallocate all stale thread states. Even if this
executes Python code, we should be safe since it executes
in the current thread, not one of the stale threads. */
Expand Down