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[3.11] gh-108987: Fix _thread.start_new_thread() race condition (#109135) (#109272)

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

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().

(cherry picked from commit 517cd82ea7)
This commit is contained in:
Victor Stinner 2023-09-11 19:33:08 +02:00 • committed by GitHub
parent 9297a72dbd
commit 82a18069a1
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5 changed files with 66 additions and 38 deletions
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25
Python/ceval_gil.h
View file

@ -185,25 +185,6 @@ drop_gil(struct _ceval_runtime_state *ceval, struct _ceval_state *ceval2,
}
/* 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 must be non-NULL. */
static inline int
tstate_must_exit(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);
return (finalizing != NULL && finalizing != tstate);
}
/* Take the GIL.
The function saves errno at entry and restores its value at exit.
@ -216,7 +197,7 @@ take_gil(PyThreadState *tstate)
assert(tstate != NULL);
if (tstate_must_exit(tstate)) {
if (_PyThreadState_MustExit(tstate)) {
/* bpo-39877: If Py_Finalize() has been called and tstate is not the
thread which called Py_Finalize(), exit immediately the thread.
@ -255,7 +236,7 @@ take_gil(PyThreadState *tstate)
_Py_atomic_load_relaxed(&gil->locked) &&
gil->switch_number == saved_switchnum)
{
if (tstate_must_exit(tstate)) {
if (_PyThreadState_MustExit(tstate)) {
MUTEX_UNLOCK(gil->mutex);
// gh-96387: If the loop requested a drop request in a previous
// iteration, reset the request. Otherwise, drop_gil() can
@ -295,7 +276,7 @@ _ready:
MUTEX_UNLOCK(gil->switch_mutex);
#endif
if (tstate_must_exit(tstate)) {
if (_PyThreadState_MustExit(tstate)) {
/* bpo-36475: If Py_Finalize() has been called and tstate is not
the thread which called Py_Finalize(), exit immediately the
thread.

26
Python/pystate.c
View file

@ -882,6 +882,10 @@ _PyThreadState_Init(PyThreadState *tstate)
void
_PyThreadState_SetCurrent(PyThreadState *tstate)
{
// gh-104690: If Python is being finalized and PyInterpreterState_Delete()
// was called, tstate becomes a dangling pointer.
assert(_PyThreadState_CheckConsistency(tstate));
_PyGILState_NoteThreadState(&tstate->interp->runtime->gilstate, tstate);
}
@ -2255,6 +2259,28 @@ _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);
return (finalizing != NULL && finalizing != tstate);
}
#ifdef __cplusplus
}
#endif