[src/trunk]: src/bin/sh Use fork() rather than vfork() when forking to run a ...

[kre <kre%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c649d135e4eb
branches:  trunk
changeset: 466434:c649d135e4eb
user:      kre <kre%NetBSD.org@localhost>
date:      Sat Dec 21 18:54:15 2019 +0000

description:
Use fork() rather than vfork() when forking to run a background
process with redirects.   If we use vfork() and a redirect hangs
(eg: opening a fifo) which the parent was intended to unhang,
then the parent never gets to continue to unhang the child.

eg:  mkfifo f; cat <f &; echo foo>f

The parent should not be waiting for a background process, even
just for its exec() to complete.   if there are no redirects there
is (should be) nothing left that might be done that will cause any
noticeable delay, so vfork() should be safe in all other cases.

diffstat:

 bin/sh/eval.c |  9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diffs (38 lines):

diff -r b799da289b99 -r c649d135e4eb bin/sh/eval.c
--- a/bin/sh/eval.c     Sat Dec 21 16:10:20 2019 +0000
+++ b/bin/sh/eval.c     Sat Dec 21 18:54:15 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: eval.c,v 1.176 2019/12/09 00:14:24 kre Exp $   */
+/*     $NetBSD: eval.c,v 1.177 2019/12/21 18:54:15 kre Exp $   */
 
 /*-
  * Copyright (c) 1993
@@ -37,7 +37,7 @@
 #if 0
 static char sccsid[] = "@(#)eval.c     8.9 (Berkeley) 6/8/95";
 #else
-__RCSID("$NetBSD: eval.c,v 1.176 2019/12/09 00:14:24 kre Exp $");
+__RCSID("$NetBSD: eval.c,v 1.177 2019/12/21 18:54:15 kre Exp $");
 #endif
 #endif /* not lint */
 
@@ -552,8 +552,8 @@
            forkshell(jp = makejob(n, 1), n, backgnd?FORK_BG:FORK_FG) == 0) {
                if (backgnd)
                        flags &=~ EV_TESTED;
+               INTON;
                redirect(n->nredir.redirect, REDIR_KEEP);
-               INTON;
                evaltree(n->nredir.n, flags | EV_EXIT);   /* never returns */
        } else if (backgnd)
                exitstatus = 0;
@@ -1086,7 +1086,8 @@
                 * child's address space is actually shared with the parent as
                 * we rely on this.
                 */
-               if (usefork == 0 && cmdentry.cmdtype == CMDNORMAL) {
+               if (usefork == 0 && cmdentry.cmdtype == CMDNORMAL &&
+                   (!cmd->ncmd.backgnd || cmd->ncmd.redirect == NULL)) {
                        pid_t   pid;
                        int serrno;