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[3.6] bpo-34658: Fix rare subprocess prexec_fn fork error. (GH-9255) #9292

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[3.6] bpo-34658: Fix rare subprocess prexec_fn fork error. (GH-9255) #9292

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c876b0c
bpo-34658: Fix rare subprocess prexec_fn fork error. (GH-9255)
gpshead Sep 13, 2018
1b5c3a1
[3.6] bpo-34658: Fix rare subprocess prexec_fn fork error. (GH-9255)
gpshead Sep 14, 2018
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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 @@ -566,6 +566,7 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
#ifdef WITH_THREAD
int import_lock_held = 0;
#endif
int saved_errno = 0;

if (!PyArg_ParseTuple(
args, "OOpO!OOiiiiiiiiiiO:fork_exec",
Expand Down Expand Up @@ -701,11 +702,10 @@ 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;
}
#ifdef WITH_THREAD
if (preexec_fn != Py_None
Expand All @@ -717,7 +717,8 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
import_lock_held = 0;
#endif

/* Parent process */
Py_XDECREF(cwd_obj2);

if (envp)
_Py_FreeCharPArray(envp);
if (argv)
Expand All @@ -731,8 +732,13 @@ 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