https://github.com/python/cpython/commit/f366e215044e348659df814c27bf70e78907df21
commit: f366e215044e348659df814c27bf70e78907df21
branch: main
author: mpage <[email protected]>
committer: colesbury <[email protected]>
date: 2024-02-16T13:29:25-05:00
summary:
gh-114271: Make `thread._rlock` thread-safe in free-threaded builds (#115102)
The ID of the owning thread (`rlock_owner`) may be accessed by
multiple threads without holding the underlying lock; relaxed
atomics are used in place of the previous loads/stores.
The number of times that the lock has been acquired (`rlock_count`)
is only ever accessed by the thread that holds the lock; we do not
need to use atomics to access it.
files:
M Include/cpython/pyatomic.h
M Include/cpython/pyatomic_gcc.h
M Include/cpython/pyatomic_msc.h
M Include/cpython/pyatomic_std.h
M Modules/_threadmodule.c
diff --git a/Include/cpython/pyatomic.h b/Include/cpython/pyatomic.h
index e10d48285367cf..9b5774190ee99e 100644
--- a/Include/cpython/pyatomic.h
+++ b/Include/cpython/pyatomic.h
@@ -360,6 +360,8 @@ _Py_atomic_load_ssize_relaxed(const Py_ssize_t *obj);
static inline void *
_Py_atomic_load_ptr_relaxed(const void *obj);
+static inline unsigned long long
+_Py_atomic_load_ullong_relaxed(const unsigned long long *obj);
// --- _Py_atomic_store ------------------------------------------------------
// Atomically performs `*obj = value` (sequential consistency)
@@ -452,6 +454,10 @@ _Py_atomic_store_ptr_relaxed(void *obj, void *value);
static inline void
_Py_atomic_store_ssize_relaxed(Py_ssize_t *obj, Py_ssize_t value);
+static inline void
+_Py_atomic_store_ullong_relaxed(unsigned long long *obj,
+ unsigned long long value);
+
// --- _Py_atomic_load_ptr_acquire / _Py_atomic_store_ptr_release ------------
diff --git a/Include/cpython/pyatomic_gcc.h b/Include/cpython/pyatomic_gcc.h
index 4095e1873d8b07..bc74149f73e83c 100644
--- a/Include/cpython/pyatomic_gcc.h
+++ b/Include/cpython/pyatomic_gcc.h
@@ -358,6 +358,10 @@ static inline void *
_Py_atomic_load_ptr_relaxed(const void *obj)
{ return (void *)__atomic_load_n((const void **)obj, __ATOMIC_RELAXED); }
+static inline unsigned long long
+_Py_atomic_load_ullong_relaxed(const unsigned long long *obj)
+{ return __atomic_load_n(obj, __ATOMIC_RELAXED); }
+
// --- _Py_atomic_store ------------------------------------------------------
@@ -476,6 +480,11 @@ static inline void
_Py_atomic_store_ssize_relaxed(Py_ssize_t *obj, Py_ssize_t value)
{ __atomic_store_n(obj, value, __ATOMIC_RELAXED); }
+static inline void
+_Py_atomic_store_ullong_relaxed(unsigned long long *obj,
+ unsigned long long value)
+{ __atomic_store_n(obj, value, __ATOMIC_RELAXED); }
+
// --- _Py_atomic_load_ptr_acquire / _Py_atomic_store_ptr_release ------------
diff --git a/Include/cpython/pyatomic_msc.h b/Include/cpython/pyatomic_msc.h
index b5c1ec94112562..6ab6401cf81e8a 100644
--- a/Include/cpython/pyatomic_msc.h
+++ b/Include/cpython/pyatomic_msc.h
@@ -712,6 +712,12 @@ _Py_atomic_load_ptr_relaxed(const void *obj)
return *(void * volatile *)obj;
}
+static inline unsigned long long
+_Py_atomic_load_ullong_relaxed(const unsigned long long *obj)
+{
+ return *(volatile unsigned long long *)obj;
+}
+
// --- _Py_atomic_store ------------------------------------------------------
@@ -886,6 +892,14 @@ _Py_atomic_store_ssize_relaxed(Py_ssize_t *obj, Py_ssize_t
value)
*(volatile Py_ssize_t *)obj = value;
}
+static inline void
+_Py_atomic_store_ullong_relaxed(unsigned long long *obj,
+ unsigned long long value)
+{
+ *(volatile unsigned long long *)obj = value;
+}
+
+
// --- _Py_atomic_load_ptr_acquire / _Py_atomic_store_ptr_release ------------
static inline void *
diff --git a/Include/cpython/pyatomic_std.h b/Include/cpython/pyatomic_std.h
index 6c934a2c5e7b64..d3004dbd24ed09 100644
--- a/Include/cpython/pyatomic_std.h
+++ b/Include/cpython/pyatomic_std.h
@@ -619,6 +619,14 @@ _Py_atomic_load_ptr_relaxed(const void *obj)
memory_order_relaxed);
}
+static inline unsigned long long
+_Py_atomic_load_ullong_relaxed(const unsigned long long *obj)
+{
+ _Py_USING_STD;
+ return atomic_load_explicit((const _Atomic(unsigned long long)*)obj,
+ memory_order_relaxed);
+}
+
// --- _Py_atomic_store ------------------------------------------------------
@@ -835,6 +843,15 @@ _Py_atomic_store_ssize_relaxed(Py_ssize_t *obj, Py_ssize_t
value)
memory_order_relaxed);
}
+static inline void
+_Py_atomic_store_ullong_relaxed(unsigned long long *obj,
+ unsigned long long value)
+{
+ _Py_USING_STD;
+ atomic_store_explicit((_Atomic(unsigned long long)*)obj, value,
+ memory_order_relaxed);
+}
+
// --- _Py_atomic_load_ptr_acquire / _Py_atomic_store_ptr_release ------------
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index da6a8bc7b120fe..ec23fe849eb031 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -11,6 +11,7 @@
#include "pycore_sysmodule.h" // _PySys_GetAttr()
#include "pycore_weakref.h" // _PyWeakref_GET_REF()
+#include <stdbool.h>
#include <stddef.h> // offsetof()
#ifdef HAVE_SIGNAL_H
# include <signal.h> // SIGINT
@@ -489,6 +490,14 @@ rlock_dealloc(rlockobject *self)
Py_DECREF(tp);
}
+static bool
+rlock_is_owned_by(rlockobject *self, PyThread_ident_t tid)
+{
+ PyThread_ident_t owner_tid =
+ _Py_atomic_load_ullong_relaxed(&self->rlock_owner);
+ return owner_tid == tid && self->rlock_count > 0;
+}
+
static PyObject *
rlock_acquire(rlockobject *self, PyObject *args, PyObject *kwds)
{
@@ -500,7 +509,7 @@ rlock_acquire(rlockobject *self, PyObject *args, PyObject
*kwds)
return NULL;
tid = PyThread_get_thread_ident_ex();
- if (self->rlock_count > 0 && tid == self->rlock_owner) {
+ if (rlock_is_owned_by(self, tid)) {
unsigned long count = self->rlock_count + 1;
if (count <= self->rlock_count) {
PyErr_SetString(PyExc_OverflowError,
@@ -513,7 +522,7 @@ rlock_acquire(rlockobject *self, PyObject *args, PyObject
*kwds)
r = acquire_timed(self->rlock_lock, timeout);
if (r == PY_LOCK_ACQUIRED) {
assert(self->rlock_count == 0);
- self->rlock_owner = tid;
+ _Py_atomic_store_ullong_relaxed(&self->rlock_owner, tid);
self->rlock_count = 1;
}
else if (r == PY_LOCK_INTR) {
@@ -544,13 +553,13 @@ rlock_release(rlockobject *self, PyObject
*Py_UNUSED(ignored))
{
PyThread_ident_t tid = PyThread_get_thread_ident_ex();
- if (self->rlock_count == 0 || self->rlock_owner != tid) {
+ if (!rlock_is_owned_by(self, tid)) {
PyErr_SetString(PyExc_RuntimeError,
"cannot release un-acquired lock");
return NULL;
}
if (--self->rlock_count == 0) {
- self->rlock_owner = 0;
+ _Py_atomic_store_ullong_relaxed(&self->rlock_owner, 0);
PyThread_release_lock(self->rlock_lock);
}
Py_RETURN_NONE;
@@ -589,7 +598,7 @@ rlock_acquire_restore(rlockobject *self, PyObject *args)
return NULL;
}
assert(self->rlock_count == 0);
- self->rlock_owner = owner;
+ _Py_atomic_store_ullong_relaxed(&self->rlock_owner, owner);
self->rlock_count = count;
Py_RETURN_NONE;
}
@@ -614,7 +623,7 @@ rlock_release_save(rlockobject *self, PyObject
*Py_UNUSED(ignored))
owner = self->rlock_owner;
count = self->rlock_count;
self->rlock_count = 0;
- self->rlock_owner = 0;
+ _Py_atomic_store_ullong_relaxed(&self->rlock_owner, 0);
PyThread_release_lock(self->rlock_lock);
return Py_BuildValue("k" Py_PARSE_THREAD_IDENT_T, count, owner);
}
@@ -628,8 +637,9 @@ static PyObject *
rlock_recursion_count(rlockobject *self, PyObject *Py_UNUSED(ignored))
{
PyThread_ident_t tid = PyThread_get_thread_ident_ex();
- return PyLong_FromUnsignedLong(
- self->rlock_owner == tid ? self->rlock_count : 0UL);
+ PyThread_ident_t owner =
+ _Py_atomic_load_ullong_relaxed(&self->rlock_owner);
+ return PyLong_FromUnsignedLong(owner == tid ? self->rlock_count : 0UL);
}
PyDoc_STRVAR(rlock_recursion_count_doc,
@@ -642,7 +652,7 @@ rlock_is_owned(rlockobject *self, PyObject
*Py_UNUSED(ignored))
{
PyThread_ident_t tid = PyThread_get_thread_ident_ex();
- if (self->rlock_count > 0 && self->rlock_owner == tid) {
+ if (rlock_is_owned_by(self, tid)) {
Py_RETURN_TRUE;
}
Py_RETURN_FALSE;
@@ -676,10 +686,12 @@ rlock_new(PyTypeObject *type, PyObject *args, PyObject
*kwds)
static PyObject *
rlock_repr(rlockobject *self)
{
+ PyThread_ident_t owner =
+ _Py_atomic_load_ullong_relaxed(&self->rlock_owner);
return PyUnicode_FromFormat(
"<%s %s object owner=%" PY_FORMAT_THREAD_IDENT_T " count=%lu at %p>",
self->rlock_count ? "locked" : "unlocked",
- Py_TYPE(self)->tp_name, self->rlock_owner,
+ Py_TYPE(self)->tp_name, owner,
self->rlock_count, self);
}
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