Author: arichardson
Date: Thu Nov 26 13:31:57 2020
New Revision: 368055
URL: https://svnweb.freebsd.org/changeset/base/368055
Log:
Significantly speed up libthr/mutex_test and make more reliable
Instead of using a simple global++ as the data race, with this change we
perform the increment by loading the global, delaying for a bit and then
storing back the incremented value. If I move the increment outside of the
mutex protected range, I can now see the data race with only 100 iterations
on amd64 in almost all cases. Before this change such a racy test almost
always passed with < 100,000 iterations and only reliably failed with the
current limit of 10 million.
I noticed this poorly written test because the mutex:mutex{2,3} and
timedmutex:mutex{2,3} tests were always timing out on our CheriBSD Jenkins.
Writing good concurrency tests is hard so I won't attempt to do so, but this
change should make the test more likely to fail if pthread_mutex_lock is not
implemented correctly while also significantly reducing the time it takes to
run these four tests. It will also reduce the time it takes for QEMU RISC-V
testsuite runs by almost 40 minutes (out of currently 7 hours).
Reviewed By: brooks, ngie
Differential Revision: https://reviews.freebsd.org/D26473
Modified:
head/contrib/netbsd-tests/lib/libpthread/t_mutex.c
Modified: head/contrib/netbsd-tests/lib/libpthread/t_mutex.c
==============================================================================
--- head/contrib/netbsd-tests/lib/libpthread/t_mutex.c Thu Nov 26 10:17:56
2020 (r368054)
+++ head/contrib/netbsd-tests/lib/libpthread/t_mutex.c Thu Nov 26 13:31:57
2020 (r368055)
@@ -35,6 +35,9 @@ __RCSID("$NetBSD: t_mutex.c,v 1.15 2017/01/16 16:23:41
#include <inttypes.h> /* For UINT16_MAX */
#include <pthread.h>
#include <stdio.h>
+#ifdef __FreeBSD__
+#include <stdlib.h>
+#endif
#include <string.h>
#include <errno.h>
#include <time.h>
@@ -128,16 +131,41 @@ ATF_TC_BODY(mutex1, tc)
PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
}
+#ifdef __FreeBSD__
+/*
+ * Increment the value using a noinline function that includes a small delay
+ * to increase the window for the RMW data race.
+ */
+__noinline static int
+increment(int value)
+{
+ for (volatile int i = 0; i < 100; i++) {
+ /* Small delay between read+write to increase chance of race */
+ __compiler_membar();
+ }
+ return value + 1;
+}
+
+static volatile bool thread2_started = false;
+#endif
+
static void *
mutex2_threadfunc(void *arg)
{
long count = *(int *)arg;
+#ifdef __FreeBSD__
+ thread2_started = true;
+#endif
printf("2: Second thread (%p). Count is %ld\n", pthread_self(), count);
while (count--) {
PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
+#ifdef __FreeBSD__
+ global_x = increment(global_x);
+#else
global_x++;
+#endif
PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
}
@@ -153,16 +181,13 @@ ATF_TC_HEAD(mutex2, tc)
atf_tc_set_md_var(tc, "timeout", "40");
#endif
#endif
-
-#ifdef __FreeBSD__
-#if defined(__riscv)
- atf_tc_set_md_var(tc, "timeout", "600");
-#endif
-#endif
}
ATF_TC_BODY(mutex2, tc)
{
int count, count2;
+#ifdef __FreeBSD__
+ int num_increments;
+#endif
pthread_t new;
void *joinval;
@@ -177,18 +202,39 @@ ATF_TC_BODY(mutex2, tc)
PTHREAD_REQUIRE(pthread_mutex_init(&mutex, NULL));
global_x = 0;
+#ifdef __FreeBSD__
+ num_increments = count = count2 = 1000;
+ if (getenv("NUM_ITERATIONS") != NULL) {
+ num_increments = count = count2 =
+ MIN(INT_MAX, strtoul(getenv("NUM_ITERATIONS"), NULL, 10));
+ }
+ printf("Will use %d iterations\n", num_increments);
+#else
count = count2 = 10000000;
+#endif
PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
+#ifdef __FreeBSD__
+ thread2_started = false;
+#endif
PTHREAD_REQUIRE(pthread_create(&new, NULL, mutex2_threadfunc, &count2));
printf("1: Thread %p\n", pthread_self());
-
+#ifdef __FreeBSD__
+ while (!thread2_started) {
+ /* Wait for thread 2 to start to increase chance of race */
+ }
+ printf("1: Unlocking to start increment loop %p\n", pthread_self());
+#endif
PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
while (count--) {
PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
+#ifdef __FreeBSD__
+ global_x = increment(global_x);
+#else
global_x++;
+#endif
PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
}
@@ -197,7 +243,14 @@ ATF_TC_BODY(mutex2, tc)
PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
printf("1: Thread joined. X was %d. Return value (long) was %ld\n",
global_x, (long)joinval);
+#ifdef __FreeBSD__
+ ATF_REQUIRE_EQ_MSG(count, -1, "%d", count);
+ ATF_REQUIRE_EQ_MSG((long)joinval, -1, "%ld", (long)joinval);
+ ATF_REQUIRE_EQ_MSG(global_x, num_increments * 2, "%d vs %d", global_x,
+ num_increments * 2);
+#else
ATF_REQUIRE_EQ(global_x, 20000000);
+#endif
#ifdef __NetBSD__
#if defined(__powerpc__)
@@ -210,16 +263,27 @@ ATF_TC_BODY(mutex2, tc)
#endif
}
+#ifdef __FreeBSD__
+static volatile bool thread3_started = false;
+#endif
+
static void *
mutex3_threadfunc(void *arg)
{
long count = *(int *)arg;
+#ifdef __FreeBSD__
+ thread3_started = true;
+#endif
printf("2: Second thread (%p). Count is %ld\n", pthread_self(), count);
while (count--) {
PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
+#ifdef __FreeBSD__
+ global_x = increment(global_x);
+#else
global_x++;
+#endif
PTHREAD_REQUIRE(pthread_mutex_unlock(&static_mutex));
}
@@ -236,16 +300,13 @@ ATF_TC_HEAD(mutex3, tc)
atf_tc_set_md_var(tc, "timeout", "40");
#endif
#endif
-
-#ifdef __FreeBSD__
-#if defined(__riscv)
- atf_tc_set_md_var(tc, "timeout", "600");
-#endif
-#endif
}
ATF_TC_BODY(mutex3, tc)
{
int count, count2;
+#ifdef __FreeBSD__
+ int num_increments;
+#endif
pthread_t new;
void *joinval;
@@ -258,18 +319,36 @@ ATF_TC_BODY(mutex3, tc)
#endif
global_x = 0;
+#ifdef __FreeBSD__
+ num_increments = count = count2 = 1000;
+ if (getenv("NUM_ITERATIONS") != NULL) {
+ num_increments = count = count2 =
+ MIN(INT_MAX, strtoul(getenv("NUM_ITERATIONS"), NULL, 10));
+ }
+ printf("Will use %d iterations\n", num_increments);
+#else
count = count2 = 10000000;
+#endif
PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
PTHREAD_REQUIRE(pthread_create(&new, NULL, mutex3_threadfunc, &count2));
printf("1: Thread %p\n", pthread_self());
-
+#ifdef __FreeBSD__
+ while (!thread3_started) {
+ /* Wait for thread 3 to start to increase chance of race */
+ }
+ printf("1: Unlocking to start increment loop %p\n", pthread_self());
+#endif
PTHREAD_REQUIRE(pthread_mutex_unlock(&static_mutex));
while (count--) {
PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
+#ifdef __FreeBSD__
+ global_x = increment(global_x);
+#else
global_x++;
+#endif
PTHREAD_REQUIRE(pthread_mutex_unlock(&static_mutex));
}
@@ -278,8 +357,14 @@ ATF_TC_BODY(mutex3, tc)
PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
printf("1: Thread joined. X was %d. Return value (long) was %ld\n",
global_x, (long)joinval);
+#ifdef __FreeBSD__
+ ATF_REQUIRE_EQ_MSG(count, -1, "%d", count);
+ ATF_REQUIRE_EQ_MSG((long)joinval, -1, "%ld", (long)joinval);
+ ATF_REQUIRE_EQ_MSG(global_x, num_increments * 2, "%d vs %d", global_x,
+ num_increments * 2);
+#else
ATF_REQUIRE_EQ(global_x, 20000000);
-
+#endif
#ifdef __NetBSD__
#if defined(__powerpc__)
/* XXX force a timeout in ppc case since an un-triggered race
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