diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst index ab9f1d88a0fc26..fca55496492685 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 a4683339820f5f..c05ea634fe5572 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, [os.fsencode(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 b58c5784283902..a5fa152715c145 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 @@ def _execute_child(self, args, executable, preexec_fn, close_fds, 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 714a2d98e9fb5e..9d9ff0a490b126 100644 --- a/Lib/test/test_capi.py +++ b/Lib/test/test_capi.py @@ -118,7 +118,7 @@ class Z(object): 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): @@ -126,7 +126,7 @@ def __len__(self): 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): @@ -136,7 +136,7 @@ def __len__(self): # 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 8603b9888bb984..99b5947e54be68 100644 --- a/Lib/test/test_subprocess.py +++ b/Lib/test/test_subprocess.py @@ -1543,6 +1543,22 @@ def test_class_getitems(self): 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 @@ def test_fork_exec(self): 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 @@ def __int__(self): 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 00000000000000..7584710af30ff8 --- /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 440c7c5b335994..2440609e31bcc2 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 pFad - Phonifier reborn

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