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gh-126688: Reinit import lock after fork#126692

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Merged
colesbury merged 3 commits into from
Nov 12, 2024
Merged

gh-126688: Reinit import lock after fork #126692

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5e86cca
gh-126688: Reinit import lock after fork
colesbury Nov 11, 2024
4bf74b8
Merge branch 'main' into gh-126688-import-lock
colesbury Nov 11, 2024
27d5db7
Only re-initialize thread id
colesbury Nov 11, 2024
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1 change: 1 addition & 0 deletions Include/internal/pycore_import.h
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Expand Up@@ -21,6 +21,7 @@ extern int _PyImport_SetModuleString(const char *name, PyObject* module);

extern void _PyImport_AcquireLock(PyInterpreterState *interp);
extern void _PyImport_ReleaseLock(PyInterpreterState *interp);
extern void _PyImport_ReInitLock(PyInterpreterState *interp);

// This is used exclusively for the sys and builtins modules:
extern int _PyImport_FixupBuiltin(
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2024-11-11-17-02-48.gh-issue-126688.QiOXUi.rst
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@@ -0,0 +1,2 @@
Fix a crash when calling :func:`os.fork` on some operating systems,
including SerenityOS.
1 change: 1 addition & 0 deletions Modules/posixmodule.c
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Expand Up@@ -678,6 +678,7 @@ PyOS_AfterFork_Child(void)
_PyEval_StartTheWorldAll(&_PyRuntime);
_PyThreadState_DeleteList(list);

_PyImport_ReInitLock(tstate->interp);
_PyImport_ReleaseLock(tstate->interp);

_PySignal_AfterFork();
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7 changes: 7 additions & 0 deletions Python/import.c
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Expand Up@@ -122,6 +122,13 @@ _PyImport_ReleaseLock(PyInterpreterState *interp)
_PyRecursiveMutex_Unlock(&IMPORT_LOCK(interp));
}

void
_PyImport_ReInitLock(PyInterpreterState *interp)
{
// gh-126688: Thread id may change after fork() on some operating systems.
IMPORT_LOCK(interp).thread = PyThread_get_thread_ident_ex();
Comment on lines +128 to +129
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@ericsnowcurrentlyericsnowcurrentlyNov 21, 2024

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Wouldn't this lead to deadlocks if some other thread happened to be holding the import lock when we forked? It seems like the child process needs to know the thread ID from which it forked.

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@colesburycolesburyNov 21, 2024

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We acquire the import lock before forking so that no other thread holds it:

cpython/Modules/posixmodule.c

Lines 618 to 624 in 09c240f

void
PyOS_BeforeFork(void)
{
PyInterpreterState*interp=_PyInterpreterState_GET();
run_at_forkers(interp->before_forkers, 1);
_PyImport_AcquireLock(interp);

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@ericsnowcurrentlyericsnowcurrentlyNov 21, 2024

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Hmm, looks like we always acquire the import lock in PyOS_BeforeFork(). It should be fine then.

}


/***************/
/* sys.modules */
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