bpo-47151: Fallback to fork when vfork fails in subprocess. (GH-32186)

miss-islington · gpshead · web-flow · commit 9ed179b07df6 · 2022-03-31T14:09:50.000-07:00
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. (cherry picked from commit 4a08c4c) Co-authored-by: Gregory P. Smith <greg@krypto.org>
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
@@ -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
@@ -681,6 +681,12 @@ 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
     {

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+When subprocess tries to use vfork, it now falls back to fork if vfork`
	`2`	`+returns an error. This allows use in situations where vfork isn't allowed`
	`3`	`+by the OS kernel.`