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[3.12] gh-105699: Use a _Py_hashtable_t for the PyModuleDef Cache (gh-106974) (gh-107412)

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gh-105699: Use a _Py_hashtable_t for the PyModuleDef Cache (gh-106974)

This fixes a crasher due to a race condition, triggered infrequently when two isolated (own GIL) subinterpreters simultaneously initialize their sys or builtins modules.  The crash happened due the combination of the "detached" thread state we were using and the "last holder" logic we use for the GIL.  It turns out it's tricky to use the same thread state for different threads.  Who could have guessed?

We solve the problem by eliminating the one object we were still sharing between interpreters.  We replace it with a low-level hashtable, using the "raw" allocator to avoid tying it to the main interpreter.

We also remove the accommodations for "detached" thread states, which were a dubious idea to start with.

(cherry picked from commit 8ba4df91ae)
This commit is contained in:
Eric Snow 2023-07-28 17:16:12 -06:00 committed by GitHub
parent e5ca2aa2c6
commit da151fdc7a
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GPG key ID: 4AEE18F83AFDEB23
6 changed files with 26595 additions and 26675 deletions
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52948
Doc/data/python3.12.abi
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File diff suppressed because it is too large Load diff

13
Include/internal/pycore_import.h
View file

@ -5,6 +5,9 @@
extern "C" {
#endif
#include "pycore_hashtable.h" // _Py_hashtable_t
#include "pycore_time.h" // _PyTime_t
struct _import_runtime_state {
/* The builtin modules (defined in config.c). */
@ -15,19 +18,15 @@ struct _import_runtime_state {
See PyInterpreterState.modules_by_index for more info. */
Py_ssize_t last_module_index;
struct {
/* A thread state tied to the main interpreter,
used exclusively for when the extensions dict is access/modified
from an arbitrary thread. */
PyThreadState main_tstate;
/* A lock to guard the dict. */
/* A lock to guard the cache. */
PyThread_type_lock mutex;
/* A dict mapping (filename, name) to PyModuleDef for modules.
/* The actual cache of (filename, name, PyModuleDef) for modules.
Only legacy (single-phase init) extension modules are added
and only if they support multiple initialization (m_size >- 0)
or are imported in the main interpreter.
This is initialized lazily in _PyImport_FixupExtensionObject().
Modules are added there and looked up in _imp.find_extension(). */
PyObject *dict;
_Py_hashtable_t *hashtable;
} extensions;
/* Package context -- the full module name for package imports */
const char * pkgcontext;

5
Include/internal/pycore_pystate.h
View file

@ -128,11 +128,6 @@ PyAPI_FUNC(void) _PyThreadState_Init(
PyThreadState *tstate);
PyAPI_FUNC(void) _PyThreadState_DeleteExcept(PyThreadState *tstate);
extern void _PyThreadState_InitDetached(PyThreadState *, PyInterpreterState *);
extern void _PyThreadState_ClearDetached(PyThreadState *);
extern void _PyThreadState_BindDetached(PyThreadState *);
extern void _PyThreadState_UnbindDetached(PyThreadState *);
/* Other */

5
Include/internal/pycore_runtime_init.h
View file

@ -41,11 +41,6 @@ extern PyTypeObject _PyExc_MemoryError;
in accordance with the specification. */ \
.autoTSSkey = Py_tss_NEEDS_INIT, \
.parser = _parser_runtime_state_INIT, \
.imports = { \
.extensions = { \
.main_tstate = _PyThreadState_INIT, \
}, \
}, \
.ceval = { \
.perf = _PyEval_RUNTIME_PERF_INIT, \
}, \

230
Python/import.c
View file

@ -2,10 +2,12 @@
#include "Python.h"
#include "pycore_hashtable.h" // _Py_hashtable_new_full()
#include "pycore_import.h" // _PyImport_BootstrapImp()
#include "pycore_initconfig.h" // _PyStatus_OK()
#include "pycore_interp.h" // struct _import_runtime_state
#include "pycore_namespace.h" // _PyNamespace_Type
#include "pycore_object.h" // _Py_SetImmortal()
#include "pycore_pyerrors.h" // _PyErr_SetString()
#include "pycore_pyhash.h" // _Py_KeyedHash()
#include "pycore_pylifecycle.h"
@ -912,35 +914,79 @@ extensions_lock_release(void)
dictionary, to avoid loading shared libraries twice.
*/
static void
_extensions_cache_init(void)
static void *
hashtable_key_from_2_strings(PyObject *str1, PyObject *str2, const char sep)
{
/* The runtime (i.e. main interpreter) must be initializing,
so we don't need to worry about the lock. */
_PyThreadState_InitDetached(&EXTENSIONS.main_tstate,
_PyInterpreterState_Main());
Py_ssize_t str1_len, str2_len;
const char *str1_data = PyUnicode_AsUTF8AndSize(str1, &str1_len);
const char *str2_data = PyUnicode_AsUTF8AndSize(str2, &str2_len);
if (str1_data == NULL || str2_data == NULL) {
return NULL;
}
/* Make sure sep and the NULL byte won't cause an overflow. */
assert(SIZE_MAX - str1_len - str2_len > 2);
size_t size = str1_len + 1 + str2_len + 1;
char *key = PyMem_RawMalloc(size);
if (key == NULL) {
PyErr_NoMemory();
return NULL;
}
strncpy(key, str1_data, str1_len);
key[str1_len] = sep;
strncpy(key + str1_len + 1, str2_data, str2_len + 1);
assert(strlen(key) == size - 1);
return key;
}
static Py_uhash_t
hashtable_hash_str(const void *key)
{
return _Py_HashBytes(key, strlen((const char *)key));
}
static int
hashtable_compare_str(const void *key1, const void *key2)
{
return strcmp((const char *)key1, (const char *)key2) == 0;
}
static void
hashtable_destroy_str(void *ptr)
{
PyMem_RawFree(ptr);
}
#define HTSEP ':'
static PyModuleDef *
_extensions_cache_get(PyObject *filename, PyObject *name)
{
PyModuleDef *def = NULL;
void *key = NULL;
extensions_lock_acquire();
PyObject *key = PyTuple_Pack(2, filename, name);
if (EXTENSIONS.hashtable == NULL) {
goto finally;
}
key = hashtable_key_from_2_strings(filename, name, HTSEP);
if (key == NULL) {
goto finally;
}
PyObject *extensions = EXTENSIONS.dict;
if (extensions == NULL) {
_Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(
EXTENSIONS.hashtable, key);
if (entry == NULL) {
goto finally;
}
def = (PyModuleDef *)PyDict_GetItemWithError(extensions, key);
def = (PyModuleDef *)entry->value;
finally:
Py_XDECREF(key);
extensions_lock_release();
if (key != NULL) {
PyMem_RawFree(key);
}
return def;
}
@ -948,124 +994,99 @@ static int
_extensions_cache_set(PyObject *filename, PyObject *name, PyModuleDef *def)
{
int res = -1;
PyThreadState *oldts = NULL;
extensions_lock_acquire();
/* Swap to the main interpreter, if necessary. This matters if
the dict hasn't been created yet or if the item isn't in the
dict yet. In both cases we must ensure the relevant objects
are created using the main interpreter. */
PyThreadState *main_tstate = &EXTENSIONS.main_tstate;
PyInterpreterState *interp = _PyInterpreterState_GET();
if (!_Py_IsMainInterpreter(interp)) {
_PyThreadState_BindDetached(main_tstate);
oldts = _PyThreadState_Swap(interp->runtime, main_tstate);
assert(!_Py_IsMainInterpreter(oldts->interp));
/* Make sure the name and filename objects are owned
by the main interpreter. */
name = PyUnicode_InternFromString(PyUnicode_AsUTF8(name));
assert(name != NULL);
filename = PyUnicode_InternFromString(PyUnicode_AsUTF8(filename));
assert(filename != NULL);
if (EXTENSIONS.hashtable == NULL) {
_Py_hashtable_allocator_t alloc = {PyMem_RawMalloc, PyMem_RawFree};
EXTENSIONS.hashtable = _Py_hashtable_new_full(
hashtable_hash_str,
hashtable_compare_str,
hashtable_destroy_str, // key
/* There's no need to decref the def since it's immortal. */
NULL, // value
&alloc
);
if (EXTENSIONS.hashtable == NULL) {
PyErr_NoMemory();
goto finally;
}
}
PyObject *key = PyTuple_Pack(2, filename, name);
void *key = hashtable_key_from_2_strings(filename, name, HTSEP);
if (key == NULL) {
goto finally;
}
PyObject *extensions = EXTENSIONS.dict;
if (extensions == NULL) {
extensions = PyDict_New();
if (extensions == NULL) {
int already_set = 0;
_Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(
EXTENSIONS.hashtable, key);
if (entry == NULL) {
if (_Py_hashtable_set(EXTENSIONS.hashtable, key, def) < 0) {
PyMem_RawFree(key);
PyErr_NoMemory();
goto finally;
}
EXTENSIONS.dict = extensions;
}
PyModuleDef *actual = (PyModuleDef *)PyDict_GetItemWithError(extensions, key);
if (PyErr_Occurred()) {
goto finally;
else {
if (entry->value == NULL) {
entry->value = def;
}
else {
/* We expect it to be static, so it must be the same pointer. */
assert((PyModuleDef *)entry->value == def);
already_set = 1;
}
PyMem_RawFree(key);
}
else if (actual != NULL) {
/* We expect it to be static, so it must be the same pointer. */
assert(def == actual);
res = 0;
goto finally;
}
/* This might trigger a resize, which is why we must switch
to the main interpreter. */
res = PyDict_SetItem(extensions, key, (PyObject *)def);
if (res < 0) {
res = -1;
goto finally;
if (!already_set) {
/* We assume that all module defs are statically allocated
and will never be freed. Otherwise, we would incref here. */
_Py_SetImmortal(def);
}
res = 0;
finally:
Py_XDECREF(key);
if (oldts != NULL) {
_PyThreadState_Swap(interp->runtime, oldts);
_PyThreadState_UnbindDetached(main_tstate);
Py_DECREF(name);
Py_DECREF(filename);
}
extensions_lock_release();
return res;
}
static int
static void
_extensions_cache_delete(PyObject *filename, PyObject *name)
{
int res = -1;
PyThreadState *oldts = NULL;
void *key = NULL;
extensions_lock_acquire();
PyObject *key = PyTuple_Pack(2, filename, name);
if (EXTENSIONS.hashtable == NULL) {
/* It was never added. */
goto finally;
}
key = hashtable_key_from_2_strings(filename, name, HTSEP);
if (key == NULL) {
goto finally;
}
PyObject *extensions = EXTENSIONS.dict;
if (extensions == NULL) {
res = 0;
_Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(
EXTENSIONS.hashtable, key);
if (entry == NULL) {
/* It was never added. */
goto finally;
}
PyModuleDef *actual = (PyModuleDef *)PyDict_GetItemWithError(extensions, key);
if (PyErr_Occurred()) {
if (entry->value == NULL) {
/* It was already removed. */
goto finally;
}
else if (actual == NULL) {
/* It was already removed or never added. */
res = 0;
goto finally;
}
/* Swap to the main interpreter, if necessary. */
PyThreadState *main_tstate = &EXTENSIONS.main_tstate;
PyInterpreterState *interp = _PyInterpreterState_GET();
if (!_Py_IsMainInterpreter(interp)) {
_PyThreadState_BindDetached(main_tstate);
oldts = _PyThreadState_Swap(interp->runtime, main_tstate);
assert(!_Py_IsMainInterpreter(oldts->interp));
}
if (PyDict_DelItem(extensions, key) < 0) {
goto finally;
}
res = 0;
/* If we hadn't made the stored defs immortal, we would decref here.
However, this decref would be problematic if the module def were
dynamically allocated, it were the last ref, and this function
were called with an interpreter other than the def's owner. */
entry->value = NULL;
finally:
if (oldts != NULL) {
_PyThreadState_Swap(interp->runtime, oldts);
_PyThreadState_UnbindDetached(main_tstate);
}
Py_XDECREF(key);
extensions_lock_release();
return res;
if (key != NULL) {
PyMem_RawFree(key);
}
}
static void
@ -1073,11 +1094,12 @@ _extensions_cache_clear_all(void)
{
/* The runtime (i.e. main interpreter) must be finalizing,
so we don't need to worry about the lock. */
// XXX assert(_Py_IsMainInterpreter(_PyInterpreterState_GET()));
Py_CLEAR(EXTENSIONS.dict);
_PyThreadState_ClearDetached(&EXTENSIONS.main_tstate);
_Py_hashtable_destroy(EXTENSIONS.hashtable);
EXTENSIONS.hashtable = NULL;
}
#undef HTSEP
static bool
check_multi_interp_extensions(PyInterpreterState *interp)
@ -1238,6 +1260,8 @@ import_find_extension(PyThreadState *tstate, PyObject *name,
PyObject *m_copy = def->m_base.m_copy;
/* Module does not support repeated initialization */
if (m_copy == NULL) {
/* It might be a core module (e.g. sys & builtins),
for which we don't set m_copy. */
m_copy = get_core_module_dict(tstate->interp, name, filename);
if (m_copy == NULL) {
return NULL;
@ -1307,9 +1331,7 @@ clear_singlephase_extension(PyInterpreterState *interp,
}
/* Clear the cached module def. */
if (_extensions_cache_delete(filename, name) < 0) {
return -1;
}
_extensions_cache_delete(filename, name);
return 0;
}
@ -3059,6 +3081,8 @@ void
_PyImport_Fini(void)
{
/* Destroy the database used by _PyImport_{Fixup,Find}Extension */
// XXX Should we actually leave them (mostly) intact, since we don't
// ever dlclose() the module files?
_extensions_cache_clear_all();
/* Use the same memory allocator as _PyImport_Init(). */
@ -3096,10 +3120,6 @@ _PyImport_Fini2(void)
PyStatus
_PyImport_InitCore(PyThreadState *tstate, PyObject *sysmod, int importlib)
{
if (_Py_IsMainInterpreter(tstate->interp)) {
_extensions_cache_init();
}
// XXX Initialize here: interp->modules and interp->import_func.
// XXX Initialize here: sys.modules and sys.meta_path.

69
Python/pystate.c
View file

@ -1632,75 +1632,6 @@ _PyThreadState_DeleteExcept(PyThreadState *tstate)
}
//-------------------------
// "detached" thread states
//-------------------------
void
_PyThreadState_InitDetached(PyThreadState *tstate, PyInterpreterState *interp)
{
_PyRuntimeState *runtime = interp->runtime;
HEAD_LOCK(runtime);
interp->threads.next_unique_id += 1;
uint64_t id = interp->threads.next_unique_id;
HEAD_UNLOCK(runtime);
init_threadstate(tstate, interp, id);
// We do not call add_threadstate().
}
void
_PyThreadState_ClearDetached(PyThreadState *tstate)
{
assert(!tstate->_status.bound);
assert(!tstate->_status.bound_gilstate);
assert(tstate->datastack_chunk == NULL);
assert(tstate->thread_id == 0);
assert(tstate->native_thread_id == 0);
assert(tstate->next == NULL);
assert(tstate->prev == NULL);
PyThreadState_Clear(tstate);
clear_datastack(tstate);
}
void
_PyThreadState_BindDetached(PyThreadState *tstate)
{
assert(!_Py_IsMainInterpreter(
current_fast_get(tstate->interp->runtime)->interp));
assert(_Py_IsMainInterpreter(tstate->interp));
bind_tstate(tstate);
/* Unlike _PyThreadState_Bind(), we do not modify gilstate TSS. */
}
void
_PyThreadState_UnbindDetached(PyThreadState *tstate)
{
assert(!_Py_IsMainInterpreter(
current_fast_get(tstate->interp->runtime)->interp));
assert(_Py_IsMainInterpreter(tstate->interp));
assert(tstate_is_alive(tstate));
assert(!tstate->_status.active);
assert(gilstate_tss_get(tstate->interp->runtime) != tstate);
unbind_tstate(tstate);
/* This thread state may be bound/unbound repeatedly,
so we must erase evidence that it was ever bound (or unbound). */
tstate->_status.bound = 0;
tstate->_status.unbound = 0;
/* We must fully unlink the thread state from any OS thread,
to allow it to be bound more than once. */
tstate->thread_id = 0;
#ifdef PY_HAVE_THREAD_NATIVE_ID
tstate->native_thread_id = 0;
#endif
}
//----------
// accessors
//----------