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bpo-34658: Fix rare subprocess prexec_fn fork error. #9255

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Merged
miss-islington merged 1 commit into from
Sep 13, 2018
Merged

bpo-34658: Fix rare subprocess prexec_fn fork error. #9255

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2018-09-13-03-59-43.bpo-34658.ykZ-ia.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix a rare interpreter unhandled exception state SystemError only seen when
using subprocess with a preexec_fn while an after_parent handler has been
registered with os.register_at_fork and the fork system call fails.
20 changes: 13 additions & 7 deletions Modules/_posixsubprocess.c
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Original file line number Diff line number Diff line change
Expand Up @@ -564,6 +564,7 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
char *const *exec_array, *const *argv = NULL, *const *envp = NULL;
Py_ssize_t arg_num;
int need_after_fork = 0;
int saved_errno = 0;

if (!PyArg_ParseTuple(
args, "OOpO!OOiiiiiiiiiiO:fork_exec",
Expand Down Expand Up @@ -700,14 +701,14 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
_exit(255);
return NULL; /* Dead code to avoid a potential compiler warning. */
}
Py_XDECREF(cwd_obj2);

/* Parent (original) process */
if (pid == -1) {
/* Capture the errno exception before errno can be clobbered. */
PyErr_SetFromErrno(PyExc_OSError);
/* Capture errno for the exception. */
saved_errno = errno;
}

/* Parent process */
Py_XDECREF(cwd_obj2);

if (need_after_fork)
PyOS_AfterFork_Parent();
if (envp)
Expand All @@ -723,8 +724,13 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
Py_XDECREF(preexec_fn_args_tuple);
Py_XDECREF(gc_module);

if (pid == -1)
return NULL; /* fork() failed. Exception set earlier. */
if (pid == -1) {
errno = saved_errno;
/* We can't call this above as PyOS_AfterFork_Parent() calls back
* into Python code which would see the unreturned error. */
PyErr_SetFromErrno(PyExc_OSError);
return NULL; /* fork() failed. */
}

return PyLong_FromPid(pid);

Expand Down