diff -r 110b95446ec2 -r 0de62758b0e1 Modules/_posixsubprocess.c
--- a/Modules/_posixsubprocess.c	Mon Jun 02 00:31:44 2014 +0100
+++ b/Modules/_posixsubprocess.c	Sun Jun 01 17:49:21 2014 -0700
@@ -182,17 +182,37 @@
     return local_max_fd;
 }
 
+static void
+setcloexec(int fd)
+{
+    long flags = fcntl(fd, F_GETFD);
+    if (-1 == flags) {
+        int errnum = errno;
+        /*
+         * This subroutine is only used for files that are opened so
+         * we can assert that EBADF shouldn't happen.
+         */
+        assert(errnum != EBADF);
+        assert(errnum != EINVAL);
+    }
 
-/* Close all file descriptors in the range from start_fd and higher
- * except for those in py_fds_to_keep.  If the range defined by
- * [start_fd, safe_get_max_fd()) is large this will take a long
- * time as it calls close() on EVERY possible fd.
+    if (-1 == fcntl(fd, F_SETFD, flags | FD_CLOEXEC)) {
+        int errnum = errno;
+        assert(errnum != EBADF);
+        assert(errnum != EINVAL);
+    }
+}
+
+/* Set to close on exec all file descriptors in the range from
+ * start_fd and higher except for those in py_fds_to_keep.  If the
+ * range defined by [start_fd, safe_get_max_fd()) is large this will
+ * take a long time as it calls fcntl() on EVERY possible fd.
  *
  * It isn't possible to know for sure what the max fd to go up to
  * is for processes with the capability of raising their maximum.
  */
 static void
-_close_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
+_setcloexec_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
 {
     long end_fd = safe_get_max_fd();
     Py_ssize_t num_fds_to_keep = PySequence_Length(py_fds_to_keep);
@@ -213,7 +233,7 @@
     }
     if (start_fd <= end_fd) {
         for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
-            while (close(fd_num) < 0 && errno == EINTR);
+            setcloexec(fd_num);
         }
     }
 }
@@ -234,8 +254,9 @@
    char           d_name[256];  /* Filename (null-terminated) */
 };
 
-/* Close all open file descriptors in the range from start_fd and higher
- * Do not close any in the sorted py_fds_to_keep list.
+/* Set to close on exec all open file descriptors in the range from
+ * start_fd and higher. Do not set to close any in the sorted
+ * py_fds_to_keep list.
  *
  * This version is async signal safe as it does not make any unsafe C library
  * calls, malloc calls or handle any locks.  It is _unfortunate_ to be forced
@@ -250,14 +271,14 @@
  * it with some cpp #define magic to work on other OSes as well if you want.
  */
 static void
-_close_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
+_setcloexec_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
 {
     int fd_dir_fd;
 
     fd_dir_fd = _Py_open(FD_DIR, O_RDONLY);
     if (fd_dir_fd == -1) {
         /* No way to get a list of open fds. */
-        _close_fds_by_brute_force(start_fd, py_fds_to_keep);
+        _setcloexec_fds_by_brute_force(start_fd, py_fds_to_keep);
         return;
     } else {
         char buffer[sizeof(struct linux_dirent64)];
@@ -274,7 +295,7 @@
                     continue;  /* Not a number. */
                 if (fd != fd_dir_fd && fd >= start_fd &&
                     !_is_fd_in_sorted_fd_sequence(fd, py_fds_to_keep)) {
-                    while (close(fd) < 0 && errno == EINTR);
+                    setcloexec(fd);
                 }
             }
         }
@@ -282,13 +303,14 @@
     }
 }
 
-#define _close_open_fds _close_open_fds_safe
+#define _setcloexec_open_fds _setcloexec_open_fds_safe
 
 #else  /* NOT (defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)) */
 
 
-/* Close all open file descriptors from start_fd and higher.
- * Do not close any in the sorted py_fds_to_keep list.
+/* Set close to close on exec all open file descriptors from start_fd
+ * and higher.  Do not set to close any in the sorted py_fds_to_keep
+ * list.
  *
  * This function violates the strict use of async signal safe functions. :(
  * It calls opendir(), readdir() and closedir().  Of these, the one most
@@ -301,7 +323,7 @@
  *   http://womble.decadent.org.uk/readdir_r-advisory.html
  */
 static void
-_close_open_fds_maybe_unsafe(long start_fd, PyObject* py_fds_to_keep)
+_setcloexec_open_fds_maybe_unsafe(long start_fd, PyObject* py_fds_to_keep)
 {
     DIR *proc_fd_dir;
 #ifndef HAVE_DIRFD
@@ -324,7 +346,7 @@
         proc_fd_dir = opendir(FD_DIR);
     if (!proc_fd_dir) {
         /* No way to get a list of open fds. */
-        _close_fds_by_brute_force(start_fd, py_fds_to_keep);
+        _setcloexec_fds_by_brute_force(start_fd, py_fds_to_keep);
     } else {
         struct dirent *dir_entry;
 #ifdef HAVE_DIRFD
@@ -339,19 +361,26 @@
                 continue;  /* Not a number. */
             if (fd != fd_used_by_opendir && fd >= start_fd &&
                 !_is_fd_in_sorted_fd_sequence(fd, py_fds_to_keep)) {
-                while (close(fd) < 0 && errno == EINTR);
+                setcloexec(fd);
             }
             errno = 0;
         }
         if (errno) {
             /* readdir error, revert behavior. Highly Unlikely. */
-            _close_fds_by_brute_force(start_fd, py_fds_to_keep);
+            _setcloexec_fds_by_brute_force(start_fd, py_fds_to_keep);
         }
         closedir(proc_fd_dir);
     }
 }
 
-#define _close_open_fds _close_open_fds_maybe_unsafe
+/*
+ * You might think this should be _close_open_fds instead but closing
+ * all file descriptors not in a list can be racy when concurrently
+ * iterating over a system's list of open file descriptors and closing
+ * files at the same time so instead we mark the files to be closed
+ * later by the system.
+ */
+#define _setcloexec_open_fds _setcloexec_open_fds_maybe_unsafe
 
 #endif  /* else NOT (defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)) */
 
@@ -471,7 +500,7 @@
     /* close FDs after executing preexec_fn, which might open FDs */
     if (close_fds) {
         /* TODO HP-UX could use pstat_getproc() if anyone cares about it. */
-        _close_open_fds(3, py_fds_to_keep);
+        _setcloexec_open_fds(3, py_fds_to_keep);
     }
 
     /* This loop matches the Lib/os.py _execvpe()'s PATH search when */