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-rw-r--r--Doc/library/subprocess.rst36
-rw-r--r--Lib/multiprocessing/util.py4
-rw-r--r--Lib/subprocess.py5
-rw-r--r--Lib/test/test_capi.py6
-rw-r--r--Lib/test/test_subprocess.py20
-rw-r--r--Misc/NEWS.d/next/Library/2022-04-25-21-33-48.gh-issue-91401._Jo4Bu.rst2
-rw-r--r--Modules/_posixsubprocess.c7
7 files changed, 70 insertions, 10 deletions
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index ab9f1d8..fca5549 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -1529,3 +1529,39 @@ runtime):
:mod:`shlex`
Module which provides function to parse and escape command lines.
+
+
+.. _disable_vfork:
+.. _disable_posix_spawn:
+
+Disabling use of ``vfork()`` or ``posix_spawn()``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+On Linux, :mod:`subprocess` defaults to using the ``vfork()`` system call
+internally when it is safe to do so rather than ``fork()``. This greatly
+improves performance.
+
+If you ever encounter a presumed highly-unusual situation where you need to
+prevent ``vfork()`` from being used by Python, you can set the
+:attr:`subprocess._USE_VFORK` attribute to a false value.
+
+ subprocess._USE_VFORK = False # See CPython issue gh-NNNNNN.
+
+Setting this has no impact on use of ``posix_spawn()`` which could use
+``vfork()`` internally within its libc implementation. There is a similar
+:attr:`subprocess._USE_POSIX_SPAWN` attribute if you need to prevent use of
+that.
+
+ subprocess._USE_POSIX_SPAWN = False # See CPython issue gh-NNNNNN.
+
+It is safe to set these to false on any Python version. They will have no
+effect on older versions when unsupported. Do not assume the attributes are
+available to read. Despite their names, a true value does not indicate that the
+corresponding function will be used, only that that it may be.
+
+Please file issues any time you have to use these private knobs with a way to
+reproduce the issue you were seeing. Link to that issue from a comment in your
+code.
+
+.. versionadded:: 3.8 ``_USE_POSIX_SPAWN``
+.. versionadded:: 3.11 ``_USE_VFORK``
diff --git a/Lib/multiprocessing/util.py b/Lib/multiprocessing/util.py
index abbc4c5..790955e 100644
--- a/Lib/multiprocessing/util.py
+++ b/Lib/multiprocessing/util.py
@@ -446,13 +446,15 @@ def _flush_std_streams():
def spawnv_passfds(path, args, passfds):
import _posixsubprocess
+ import subprocess
passfds = tuple(sorted(map(int, passfds)))
errpipe_read, errpipe_write = os.pipe()
try:
return _posixsubprocess.fork_exec(
args, [path], True, passfds, None, None,
-1, -1, -1, -1, -1, -1, errpipe_read, errpipe_write,
- False, False, None, None, None, -1, None)
+ False, False, None, None, None, -1, None,
+ subprocess._USE_VFORK)
finally:
os.close(errpipe_read)
os.close(errpipe_write)
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index b58c578..a5fa152 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -702,7 +702,10 @@ def _use_posix_spawn():
return False
+# These are primarily fail-safe knobs for negatives. A True value does not
+# guarantee the given libc/syscall API will be used.
_USE_POSIX_SPAWN = _use_posix_spawn()
+_USE_VFORK = True
class Popen:
@@ -1792,7 +1795,7 @@ class Popen:
errpipe_read, errpipe_write,
restore_signals, start_new_session,
gid, gids, uid, umask,
- preexec_fn)
+ preexec_fn, _USE_VFORK)
self._child_created = True
finally:
# be sure the FD is closed no matter what
diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index 5f5d351..1aed9b7 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -140,7 +140,7 @@ class CAPITest(unittest.TestCase):
def __len__(self):
return 1
self.assertRaises(TypeError, _posixsubprocess.fork_exec,
- 1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21)
+ 1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22)
# Issue #15736: overflow in _PySequence_BytesToCharpArray()
class Z(object):
def __len__(self):
@@ -148,7 +148,7 @@ class CAPITest(unittest.TestCase):
def __getitem__(self, i):
return b'x'
self.assertRaises(MemoryError, _posixsubprocess.fork_exec,
- 1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21)
+ 1,Z(),3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22)
@unittest.skipUnless(_posixsubprocess, '_posixsubprocess required for this test.')
def test_subprocess_fork_exec(self):
@@ -158,7 +158,7 @@ class CAPITest(unittest.TestCase):
# Issue #15738: crash in subprocess_fork_exec()
self.assertRaises(TypeError, _posixsubprocess.fork_exec,
- Z(),[b'1'],3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21)
+ Z(),[b'1'],3,(1, 2),5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22)
@unittest.skipIf(MISSING_C_DOCSTRINGS,
"Signature information for builtins requires docstrings")
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 8603b98..99b5947 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1543,6 +1543,22 @@ class ProcessTestCase(BaseTestCase):
self.assertIsInstance(subprocess.Popen[bytes], types.GenericAlias)
self.assertIsInstance(subprocess.CompletedProcess[str], types.GenericAlias)
+ @unittest.skipIf(not sysconfig.get_config_var("HAVE_VFORK"),
+ "vfork() not enabled by configure.")
+ @mock.patch("subprocess._fork_exec")
+ def test__use_vfork(self, mock_fork_exec):
+ self.assertTrue(subprocess._USE_VFORK) # The default value regardless.
+ mock_fork_exec.side_effect = RuntimeError("just testing args")
+ with self.assertRaises(RuntimeError):
+ subprocess.run([sys.executable, "-c", "pass"])
+ mock_fork_exec.assert_called_once()
+ self.assertTrue(mock_fork_exec.call_args.args[-1])
+ with mock.patch.object(subprocess, '_USE_VFORK', False):
+ with self.assertRaises(RuntimeError):
+ subprocess.run([sys.executable, "-c", "pass"])
+ self.assertFalse(mock_fork_exec.call_args_list[-1].args[-1])
+
+
class RunFuncTestCase(BaseTestCase):
def run_python(self, code, **kwargs):
"""Run Python code in a subprocess using subprocess.run"""
@@ -3107,7 +3123,7 @@ class POSIXProcessTestCase(BaseTestCase):
1, 2, 3, 4,
True, True,
False, [], 0, -1,
- func)
+ func, False)
# Attempt to prevent
# "TypeError: fork_exec() takes exactly N arguments (M given)"
# from passing the test. More refactoring to have us start
@@ -3156,7 +3172,7 @@ class POSIXProcessTestCase(BaseTestCase):
1, 2, 3, 4,
True, True,
None, None, None, -1,
- None)
+ None, "no vfork")
self.assertIn('fds_to_keep', str(c.exception))
finally:
if not gc_enabled:
diff --git a/Misc/NEWS.d/next/Library/2022-04-25-21-33-48.gh-issue-91401._Jo4Bu.rst b/Misc/NEWS.d/next/Library/2022-04-25-21-33-48.gh-issue-91401._Jo4Bu.rst
new file mode 100644
index 0000000..7584710
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-04-25-21-33-48.gh-issue-91401._Jo4Bu.rst
@@ -0,0 +1,2 @@
+Provide a way to disable :mod:`subprocess` use of ``vfork()`` just in case
+it is ever needed and document the existing mechanism for ``posix_spawn()``.
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 440c7c5..2440609 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -751,9 +751,10 @@ subprocess_fork_exec(PyObject *module, PyObject *args)
Py_ssize_t arg_num, num_groups = 0;
int need_after_fork = 0;
int saved_errno = 0;
+ int allow_vfork;
if (!PyArg_ParseTuple(
- args, "OOpO!OOiiiiiiiiiiOOOiO:fork_exec",
+ args, "OOpO!OOiiiiiiiiiiOOOiOp:fork_exec",
&process_args, &executable_list,
&close_fds, &PyTuple_Type, &py_fds_to_keep,
&cwd_obj, &env_list,
@@ -761,7 +762,7 @@ subprocess_fork_exec(PyObject *module, PyObject *args)
&errread, &errwrite, &errpipe_read, &errpipe_write,
&restore_signals, &call_setsid,
&gid_object, &groups_list, &uid_object, &child_umask,
- &preexec_fn))
+ &preexec_fn, &allow_vfork))
return NULL;
if ((preexec_fn != Py_None) &&
@@ -940,7 +941,7 @@ subprocess_fork_exec(PyObject *module, PyObject *args)
#ifdef VFORK_USABLE
/* Use vfork() only if it's safe. See the comment above child_exec(). */
sigset_t old_sigs;
- if (preexec_fn == Py_None &&
+ if (preexec_fn == Py_None && allow_vfork &&
!call_setuid && !call_setgid && !call_setgroups) {
/* Block all signals to ensure that no signal handlers are run in the
* child process while it shares memory with us. Note that signals
generated by cgit v0.12 at 2025-03-13 13:58:39 (GMT)