Add unix_sorflush, a regression test for the following scenario:

- Process (a) is blocked in read on a socket waiting on data.
 - Process (b) is blocked in shutdown() on a socket waiting on (a).
 - Process (c) delivers a signal to (b) interrupting its wait.

When the signal is delivered, the kernel panics as sblock() fails in
sorflush().  Even if it didn't panic, shutdown() would block potentially
indefinitely waiting for recv() to succeeded.  Fixes to follow.

Reported by:	Jos Backus <jos at catnook dot com>

tools/regression/sockets/unix_sorflush/Makefile

@@ -0,0 +1,7 @@
+# $FreeBSD$
+
+PROG=	unix_sorflush
+NO_MAN=
+WARNS=	3
+
+.include <bsd.prog.mk>

tools/regression/sockets/unix_sorflush/unix_sorflush.c

@@ -0,0 +1,99 @@
+/*-
+ * Copyright (c) 2008 Robert N. M. Watson
+ * All rights reserved.
+ *
+ * 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.
+ */
+
+/*
+ * Reproduce a race in which:
+ *
+ * - Process (a) is blocked in read on a socket waiting on data.
+ * - Process (b) is blocked in shutdown() on a socket waiting on (a).
+ * - Process (c) delivers a signal to (b) interrupting its wait.
+ *
+ * This race is premised on shutdown() not interrupting (a) properly, and the
+ * signal to (b) causing problems in the kernel.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/socket.h>
+
+#include <err.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static void
+receive_and_exit(int s)
+{
+	ssize_t ssize;
+	char ch;
+
+	ssize = recv(s, &ch, sizeof(ch), 0);
+	if (ssize < 0)
+		err(-1, "receive_and_exit: recv");
+	exit(0);
+}
+
+static void
+shutdown_and_exit(int s)
+{
+
+	if (shutdown(s, SHUT_RD) < 0)
+		err(-1, "shutdown_and_exit: shutdown");
+	exit(0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	pid_t pida, pidb;
+	int sv[2];
+
+	if (socketpair(PF_LOCAL, SOCK_STREAM, 0, sv) < 0)
+		err(-1, "socketpair");
+
+	pida = fork();
+	if (pida < 0)
+		err(-1, "fork");
+	if (pida == 0)
+		receive_and_exit(sv[1]);
+	sleep(1);
+	pidb = fork();
+	if (pidb < 0) {
+		warn("fork");
+		(void)kill(pida, SIGKILL);
+		exit(-1);
+	}
+	if (pidb == 0)
+		shutdown_and_exit(sv[1]);
+	sleep(1);
+	if (kill(pidb, SIGKILL) < 0)
+		err(-1, "kill");
+	sleep(1);
+	printf("ok 1 - unix_sorflush\n");
+	exit(0);
+}