From 777d66eb152d945791241f8d43f461aaf0abc097 Mon Sep 17 00:00:00 2001
From: Glenn Strauss <gstrauss@gluelogic.com>
Date: Sat, 17 Sep 2016 21:52:06 -0400
Subject: [PATCH] context1.c - better end-of-stream, signal handling

Addresses "slave write failed: Broken pipe; aborting"

There are two processes that are alternating reading and writing
a sequence number of sizeof(unsigned long) size, which is 4 bytes
on 32-bit ILP32 ABI and 8 bytes on 64-bit LP64 ABI.  The read/write
passing of incrementing sequence number occurs in infinite loop
until an alarm signals each process.  There is a race condition
where a signal delivered to one process might close the pipes while
the second process was still attempting to read or write from the
pipes, and before the second process was interrupted with SIGALRM.

This patch fixes the race condition that occurs at the end of the
test run, after the first SIGALRM is delivered.

This patch does not address the paranoid possibility that read() or
write() of 4 or 8 bytes might theoretically be a partial read() or
write(), but that is extremely unlikely except in the case of a signal
being delivered, and the only signal expected is SIGALRM, and the
processing of SIGALRM by report() function does not return.  (This
patch adds code to ignore SIGPIPE, so SIGALRM is the only expected
signal.)

github: fixes #1
---
 UnixBench/src/context1.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/UnixBench/src/context1.c b/UnixBench/src/context1.c
index 542a25f..267b790 100644
--- a/UnixBench/src/context1.c
+++ b/UnixBench/src/context1.c
@@ -56,6 +56,7 @@ char	*argv[];
 	/* set up alarm call */
 	iter = 0;
 	wake_me(duration, report);
+	signal(SIGPIPE, SIG_IGN);
 
 	if (pipe(p1) || pipe(p2)) {
 		perror("pipe create failed");
@@ -66,12 +67,20 @@ char	*argv[];
 		/* master, write p1 & read p2 */
 		close(p1[0]); close(p2[1]);
 		while (1) {
-			if (write(p1[1], (char *)&iter, sizeof(iter)) != sizeof(iter)) {
-				if ((errno != 0) && (errno != EINTR))
+			if ((ret = write(p1[1], (char *)&iter, sizeof(iter))) != sizeof(iter)) {
+				if ((ret == -1) && (errno == EPIPE)) {
+					alarm(0);
+					report(); /* does not return */
+				}
+				if ((ret == -1) && (errno != 0) && (errno != EINTR))
 					perror("master write failed");
 				exit(1);
 			}
 			if ((ret = read(p2[0], (char *)&check, sizeof(check))) != sizeof(check)) {
+				if ((ret == 0)) { /* end-of-stream */
+					alarm(0);
+					report(); /* does not return */
+				}
 				if ((ret == -1) && (errno != 0) && (errno != EINTR))
 					perror("master read failed");
 				exit(1);
@@ -92,6 +101,10 @@ char	*argv[];
 		close(p1[1]); close(p2[0]);
 		while (1) {
 			if ((ret = read(p1[0], (char *)&check, sizeof(check))) != sizeof(check)) {
+				if ((ret == 0)) { /* end-of-stream */
+					alarm(0);
+					report(); /* does not return */
+				}
 				if ((ret == -1) && (errno != 0) && (errno != EINTR))
 					perror("slave read failed");
 				exit(1);
@@ -101,8 +114,12 @@ char	*argv[];
 					iter, check);
 				exit(2);
 			}
-			if (write(p2[1], (char *)&iter1, sizeof(iter1)) != sizeof(check)) {
-				if ((errno != 0) && (errno != EINTR))
+			if ((ret = write(p2[1], (char *)&iter1, sizeof(iter1))) != sizeof(check)) {
+				if ((ret == -1) && (errno == EPIPE)) {
+					alarm(0);
+					report(); /* does not return */
+				}
+				if ((ret == -1) && (errno != 0) && (errno != EINTR))
 					perror("slave write failed");
 				exit(1);
 			}