[issue42540] Debug pymalloc crash when using os.fork() [regression]

[Steve Stagg]

Steve Stagg <stestagg at gmail.com> added the comment:

So, I'm not an allocator/init/teardown expert, but it looks like: When you fork, PyRuntimeState creates a new mutex, explicitly using the default allocator (without the debug allocator active)..


#ifdef HAVE_FORK
/* This function is called from PyOS_AfterFork_Child to ensure that
   newly created child processes do not share locks with the parent. */
PyStatus
_PyRuntimeState_ReInitThreads(_PyRuntimeState *runtime)
{
    // This was initially set in _PyRuntimeState_Init().
    runtime->main_thread = PyThread_get_thread_ident();

    /* Force default allocator, since _PyRuntimeState_Fini() must
       use the same allocator than this function. */
    PyMemAllocatorEx old_alloc;
    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);

    int reinit_interp = _PyThread_at_fork_reinit(&runtime->interpreters.mutex);
    int reinit_main_id = _PyThread_at_fork_reinit(&runtime->interpreters.main->id_mutex);
    int reinit_xidregistry = _PyThread_at_fork_reinit(&runtime->xidregistry.mutex);

    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);

    if (reinit_interp < 0
        || reinit_main_id < 0
        || reinit_xidregistry < 0)
    {
        return _PyStatus_ERR("Failed to reinitialize runtime locks");

    }
    return _PyStatus_OK();
}
#endif


But the PyInterpreterState_Delete function does not do this:

if (interp->id_mutex != NULL) {
    PyThread_free_lock(interp->id_mutex);
}


Which causes it to try to use the debug allocator to free, and hence crash..

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<https://bugs.python.org/issue42540>
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