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gh-111924: Fix data races when swapping allocators (gh-130287)

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CPython current temporarily changes `PYMEM_DOMAIN_RAW` to the default
allocator during initialization and shutdown. The motivation is to
ensure that core runtime structures are allocated and freed using the
same allocator. However, modifying the current allocator changes global
state and is not thread-safe even with the GIL. Other threads may be
allocating or freeing objects use PYMEM_DOMAIN_RAW; they are not
required to hold the GIL to call PyMem_RawMalloc/PyMem_RawFree.

This adds new internal-only functions like `_PyMem_DefaultRawMalloc`
that aren't affected by calls to `PyMem_SetAllocator()`, so they're
appropriate for Python runtime initialization and finalization. Use
these calls in places where we previously swapped to the default raw
allocator.
This commit is contained in:
Sam Gross 2025-02-20 11:31:15 -05:00 • committed by GitHub
parent 568db400ff
commit ca22147547
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GPG key ID: B5690EEEBB952194
9 changed files with 155 additions and 154 deletions
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22
Python/sysmodule.c
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@ -29,7 +29,7 @@ Data members:
#include "pycore_pyerrors.h" // _PyErr_GetRaisedException()
#include "pycore_pylifecycle.h" // _PyErr_WriteUnraisableDefaultHook()
#include "pycore_pymath.h" // _PY_SHORT_FLOAT_REPR
#include "pycore_pymem.h" // _PyMem_SetDefaultAllocator()
#include "pycore_pymem.h" // _PyMem_DefaultRawFree()
#include "pycore_pystate.h" // _PyThreadState_GET()
#include "pycore_pystats.h" // _Py_PrintSpecializationStats()
#include "pycore_structseq.h" // _PyStructSequence_InitBuiltinWithFlags()
@ -2724,22 +2724,17 @@ _alloc_preinit_entry(const wchar_t *value)
/* To get this to work, we have to initialize the runtime implicitly */
_PyRuntime_Initialize();
/* Force default allocator, so we can ensure that it also gets used to
/* Use the default allocator, so we can ensure that it also gets used to
* destroy the linked list in _clear_preinit_entries.
*/
PyMemAllocatorEx old_alloc;
_PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
_Py_PreInitEntry node = PyMem_RawCalloc(1, sizeof(*node));
_Py_PreInitEntry node = _PyMem_DefaultRawCalloc(1, sizeof(*node));
if (node != NULL) {
node->value = _PyMem_RawWcsdup(value);
node->value = _PyMem_DefaultRawWcsdup(value);
if (node->value == NULL) {
PyMem_RawFree(node);
_PyMem_DefaultRawFree(node);
node = NULL;
};
};
PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
return node;
}
@ -2771,15 +2766,12 @@ _clear_preinit_entries(_Py_PreInitEntry *optionlist)
_Py_PreInitEntry current = *optionlist;
*optionlist = NULL;
/* Deallocate the nodes and their contents using the default allocator */
PyMemAllocatorEx old_alloc;
_PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
while (current != NULL) {
_Py_PreInitEntry next = current->next;
PyMem_RawFree(current->value);
PyMem_RawFree(current);
_PyMem_DefaultRawFree(current->value);
_PyMem_DefaultRawFree(current);
current = next;
}
PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
}