From 4a08c4c469d36f99d3a5e0f17ad82ab35dcf2835 Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith" <greg@krypto.org>
Date: Thu, 31 Mar 2022 13:42:28 -0700
Subject: [PATCH] bpo-47151: Fallback to fork when vfork fails in subprocess.
 (GH-32186)

bpo-47151: Fallback to fork when vfork fails in subprocess. An OS kernel can specifically decide to disallow vfork() in a process. No need for that to prevent us from launching subprocesses.
---
 .../next/Library/2022-03-30-01-17-43.bpo-47151.z-nQkR.rst   | 3 +++
 Modules/_posixsubprocess.c                                  | 6 ++++++
 2 files changed, 9 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2022-03-30-01-17-43.bpo-47151.z-nQkR.rst

diff --git a/Misc/NEWS.d/next/Library/2022-03-30-01-17-43.bpo-47151.z-nQkR.rst b/Misc/NEWS.d/next/Library/2022-03-30-01-17-43.bpo-47151.z-nQkR.rst
new file mode 100644
index 00000000000000..d4d02459d35de1
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-03-30-01-17-43.bpo-47151.z-nQkR.rst
@@ -0,0 +1,3 @@
+When subprocess tries to use vfork, it now falls back to fork if vfork
+returns an error. This allows use in situations where vfork isn't allowed
+by the OS kernel.
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index de599f8c970e38..440c7c5b335994 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -685,6 +685,12 @@ do_fork_exec(char *const exec_array[],
         assert(preexec_fn == Py_None);
 
         pid = vfork();
+        if (pid == -1) {
+            /* If vfork() fails, fall back to using fork(). When it isn't
+             * allowed in a process by the kernel, vfork can return -1
+             * with errno EINVAL. https://bugs.python.org/issue47151. */
+            pid = fork();
+        }
     } else
 #endif
     {