Index: user/pho/stress2/misc/mkfifo8.sh
===================================================================
--- user/pho/stress2/misc/mkfifo8.sh	(nonexistent)
+++ user/pho/stress2/misc/mkfifo8.sh	(revision 349553)
@@ -0,0 +1,202 @@
+#!/bin/sh
+
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2019 Dell EMC Isilon
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+# $FreeBSD$
+#
+
+# Regression test for https://reviews.freebsd.org/D20784
+# "Fix mutual exclusion in pipe_direct_write()"
+# https://people.freebsd.org/~pho/stress/log/mkfifo8.txt
+
+# Reported by syzbot+21811cc0a89b2a87a9e7@syzkaller.appspotmail.com
+# Test scenario suggestion by markj@
+# Fixed by r349546
+
+. ../default.cfg
+[ `id -u ` -ne 0 ] && echo "Must be root!" && exit 1
+
+dir=/tmp
+odir=`pwd`
+cd $dir
+sed '1,/^EOF/d' < $odir/$0 > $dir/mkfifo8.c
+mycc -o mkfifo8 -Wall -Wextra -O0 -g mkfifo8.c || exit 1
+rm -f mkfifo8.c
+cd $odir
+
+set -e
+mount | grep -q "on $mntpoint " && umount -f $mntpoint
+[ -c /dev/md$mdstart ] && mdconfig -d -u $mdstart
+mdconfig -a -t swap -s 1g -u $mdstart
+newfs $newfs_flags /dev/md$mdstart > /dev/null
+mount /dev/md$mdstart $mntpoint
+set +e
+
+cd $mntpoint
+$dir/mkfifo8; s=$?
+cd $odir
+
+while mount | grep -q "on $mntpoint "; do
+        umount $mntpoint || sleep 1
+done
+mdconfig -d -u $mdstart
+rm -rf /tmp/mkfifo8
+exit $s
+
+EOF
+#include <sys/param.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+#include <machine/atomic.h>
+
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+
+#define ACT 1
+#define NPROCS 64
+#define PARALLEL 4
+#define RUNTIME 60
+#define SIZ 8192
+#define SYNC 0
+
+static volatile u_int *share;
+static int fd;
+static char cp[SIZ];
+
+static void
+tw(void)
+{
+	int r;
+
+        atomic_add_int(&share[ACT], 1);
+	r = write(fd, cp, SIZ);
+	if (r == -1)
+		warn("write");
+
+	_exit(0);
+}
+
+static void
+tr(void)
+{
+	int i, r;
+	char cp[SIZ];
+
+	while (share[ACT] < NPROCS / 2)
+		usleep(10);
+	for (i = 0; i < NPROCS; i++) {
+		r = read(fd, cp, SIZ);
+		if (r == -1)
+			warn("read");
+	}
+
+	_exit(0);
+}
+
+static void
+test(void)
+{
+        pid_t pid[NPROCS + 1];
+        int i;
+        char file[80];
+
+        atomic_add_int(&share[SYNC], 1);
+        while (share[SYNC] != PARALLEL)
+                ;
+
+        snprintf(file, sizeof(file), "fifo.%d", getpid());
+	if (mkfifo(file, DEFFILEMODE) == -1)
+                err(1, "mkfifo(%s)", file);
+        if ((fd = open(file, O_RDWR)) == -1)
+                err(1, "open(%s)", file);
+
+	for (i = 0; i < NPROCS; i++) {
+		if ((pid[i] = fork()) == 0)
+			tw();
+	}
+	if ((pid[NPROCS] = fork()) == 0)
+		tr();
+
+	for (i = 0; i < NPROCS + 1; i++) {
+		if (waitpid(pid[i], NULL, 0) != pid[i])
+			err(1, "waitpid");
+	}
+        close(fd);
+        unlink(file);
+
+        _exit(0);
+}
+
+int
+main(void)
+{
+        pid_t pids[PARALLEL];
+        size_t len;
+        time_t start;
+        int e, i, status;
+
+        e = 0;
+        len = PAGE_SIZE;
+        if ((share = mmap(NULL, len, PROT_READ | PROT_WRITE,
+            MAP_ANON | MAP_SHARED, -1, 0)) == MAP_FAILED)
+                err(1, "mmap");
+
+	for (i = 0; i < SIZ; i += PAGE_SIZE)
+		cp[i] = 1;
+        start = time(NULL);
+        while ((time(NULL) - start) < RUNTIME && e == 0) {
+                share[SYNC] = 0;
+                share[ACT] = 0;
+                for (i = 0; i < PARALLEL; i++) {
+                        if ((pids[i] = fork()) == 0)
+                                test();
+                        if (pids[i] == -1)
+                                err(1, "fork()");
+                }
+                for (i = 0; i < PARALLEL; i++) {
+                        if (waitpid(pids[i], &status, 0) == -1)
+                                err(1, "waitpid(%d)", pids[i]);
+                        if (status != 0) {
+                                if (WIFSIGNALED(status))
+                                        fprintf(stderr,
+                                            "pid %d exit signal %d\n",
+                                            pids[i], WTERMSIG(status));
+                        }
+                        e += status == 0 ? 0 : 1;
+                }
+        }
+
+        return (e);
+}