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gh-144763: Don't detach the GIL in tracemalloc #144779

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gh-144763: Don't detach the GIL in tracemalloc #144779

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gh-144763: Don't detach the GIL in tracemalloc
vstinner Feb 13, 2026
a91fc22
Fix race condition in _PyTraceMalloc_Stop()
vstinner Feb 13, 2026
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-02-13-11-14-18.gh-issue-144763.cDwnEE.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a race condition in :mod:`tracemalloc`: it no longer detachs the GIL to
acquire its internal lock. Patch by Victor Stinner.
24 changes: 17 additions & 7 deletions Python/tracemalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@ static int _PyTraceMalloc_TraceRef(PyObject *op, PyRefTracerEvent event,
the GIL held from PyMem_RawFree(). It cannot acquire the lock because it
would introduce a deadlock in _PyThreadState_DeleteCurrent(). */
#define tables_lock _PyRuntime.tracemalloc.tables_lock
#define TABLES_LOCK() PyMutex_Lock(&tables_lock)
#define TABLES_LOCK() PyMutex_LockFlags(&tables_lock, _Py_LOCK_DONT_DETACH)
#define TABLES_UNLOCK() PyMutex_Unlock(&tables_lock)


Expand Down Expand Up @@ -224,13 +224,20 @@ tracemalloc_get_frame(_PyInterpreterFrame *pyframe, frame_t *frame)
assert(PyStackRef_CodeCheck(pyframe->f_executable));
frame->filename = &_Py_STR(anon_unknown);

int lineno = PyUnstable_InterpreterFrame_GetLine(pyframe);
int lineno = -1;
PyCodeObject *code = _PyFrame_GetCode(pyframe);
// PyUnstable_InterpreterFrame_GetLine() cannot but used, since it uses
// a critical section which can trigger a deadlock.
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@kumaraditya303 kumaraditya303 Feb 14, 2026 •
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I think the problem is that critical sections requires an active thread state and this code can be called with detached thread state iirc.

int lasti = _PyFrame_SafeGetLasti(pyframe);
if (lasti >= 0) {
lineno = _PyCode_SafeAddr2Line(code, lasti);
}
if (lineno < 0) {
lineno = 0;
}
frame->lineno = (unsigned int)lineno;

PyObject *filename = _PyFrame_GetCode(pyframe)->co_filename;
PyObject *filename = code->co_filename;
if (filename == NULL) {
#ifdef TRACE_DEBUG
tracemalloc_error("failed to get the filename of the code object");
Expand Down Expand Up @@ -863,7 +870,8 @@ _PyTraceMalloc_Stop(void)
TABLES_LOCK();

if (!tracemalloc_config.tracing) {
goto done;
TABLES_UNLOCK();
return;
}

/* stop tracing Python memory allocations */
Expand All @@ -880,10 +888,12 @@ _PyTraceMalloc_Stop(void)
raw_free(tracemalloc_traceback);
tracemalloc_traceback = NULL;

(void)PyRefTracer_SetTracer(NULL, NULL);

done:
TABLES_UNLOCK();

// Call it after TABLES_UNLOCK() since it calls _PyEval_StopTheWorldAll()
// which would lead to a deadlock with TABLES_LOCK() which doesn't release
// the GIL.
(void)PyRefTracer_SetTracer(NULL, NULL);
}


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