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gh-108987: Fix _thread.start_new_thread() race condition (#109135)

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Fix _thread.start_new_thread() race condition. If a thread is created
during Python finalization, the newly spawned thread now exits
immediately instead of trying to access freed memory and lead to a
crash.

thread_run() calls PyEval_AcquireThread() which checks if the thread
must exit. The problem was that tstate was dereferenced earlier in
_PyThreadState_Bind() which leads to a crash most of the time.

Move _PyThreadState_CheckConsistency() from thread_run() to
_PyThreadState_Bind().
This commit is contained in:
Victor Stinner 2023-09-11 17:27:03 +02:00 • committed by GitHub
parent c0f488b88f
commit 517cd82ea7
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5 changed files with 69 additions and 41 deletions
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29
Python/pystate.c
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@ -1907,6 +1907,10 @@ PyThreadState_Swap(PyThreadState *newts)
void
_PyThreadState_Bind(PyThreadState *tstate)
{
// gh-104690: If Python is being finalized and PyInterpreterState_Delete()
// was called, tstate becomes a dangling pointer.
assert(_PyThreadState_CheckConsistency(tstate));
bind_tstate(tstate);
// This makes sure there's a gilstate tstate bound
// as soon as possible.
@ -2908,6 +2912,31 @@ _PyThreadState_CheckConsistency(PyThreadState *tstate)
#endif
// Check if a Python thread must exit immediately, rather than taking the GIL
// if Py_Finalize() has been called.
//
// When this function is called by a daemon thread after Py_Finalize() has been
// called, the GIL does no longer exist.
//
// tstate can be a dangling pointer (point to freed memory): only tstate value
// is used, the pointer is not deferenced.
//
// tstate must be non-NULL.
int
_PyThreadState_MustExit(PyThreadState *tstate)
{
/* bpo-39877: Access _PyRuntime directly rather than using
tstate->interp->runtime to support calls from Python daemon threads.
After Py_Finalize() has been called, tstate can be a dangling pointer:
point to PyThreadState freed memory. */
PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(&_PyRuntime);
if (finalizing == NULL) {
finalizing = _PyInterpreterState_GetFinalizing(tstate->interp);
}
return (finalizing != NULL && finalizing != tstate);
}
#ifdef __cplusplus
}
#endif