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
This commit is contained in:
Alex Richardson
parent
569da02b0c
commit
371f152c7f
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=368055
@ -35,6 +35,9 @@ __RCSID("$NetBSD: t_mutex.c,v 1.15 2017/01/16 16:23:41 christos Exp $");
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#include <inttypes.h> /* For UINT16_MAX */
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#include <pthread.h>
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#include <stdio.h>
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#ifdef __FreeBSD__
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#include <stdlib.h>
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#endif
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#include <string.h>
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#include <errno.h>
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#include <time.h>
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@ -128,16 +131,41 @@ ATF_TC_BODY(mutex1, tc)
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PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
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}
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#ifdef __FreeBSD__
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/*
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* Increment the value using a noinline function that includes a small delay
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* to increase the window for the RMW data race.
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*/
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__noinline static int
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increment(int value)
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{
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for (volatile int i = 0; i < 100; i++) {
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/* Small delay between read+write to increase chance of race */
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__compiler_membar();
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}
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return value + 1;
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}
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static volatile bool thread2_started = false;
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#endif
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static void *
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mutex2_threadfunc(void *arg)
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{
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long count = *(int *)arg;
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#ifdef __FreeBSD__
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thread2_started = true;
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#endif
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printf("2: Second thread (%p). Count is %ld\n", pthread_self(), count);
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while (count--) {
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PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
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#ifdef __FreeBSD__
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global_x = increment(global_x);
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#else
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global_x++;
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#endif
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PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
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}
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@ -153,16 +181,13 @@ ATF_TC_HEAD(mutex2, tc)
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atf_tc_set_md_var(tc, "timeout", "40");
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#endif
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#endif
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#ifdef __FreeBSD__
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#if defined(__riscv)
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atf_tc_set_md_var(tc, "timeout", "600");
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#endif
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#endif
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}
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ATF_TC_BODY(mutex2, tc)
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{
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int count, count2;
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#ifdef __FreeBSD__
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int num_increments;
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#endif
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pthread_t new;
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void *joinval;
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@ -177,18 +202,39 @@ ATF_TC_BODY(mutex2, tc)
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PTHREAD_REQUIRE(pthread_mutex_init(&mutex, NULL));
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global_x = 0;
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#ifdef __FreeBSD__
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num_increments = count = count2 = 1000;
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if (getenv("NUM_ITERATIONS") != NULL) {
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num_increments = count = count2 =
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MIN(INT_MAX, strtoul(getenv("NUM_ITERATIONS"), NULL, 10));
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}
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printf("Will use %d iterations\n", num_increments);
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#else
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count = count2 = 10000000;
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#endif
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PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
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#ifdef __FreeBSD__
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thread2_started = false;
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#endif
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PTHREAD_REQUIRE(pthread_create(&new, NULL, mutex2_threadfunc, &count2));
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printf("1: Thread %p\n", pthread_self());
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#ifdef __FreeBSD__
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while (!thread2_started) {
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/* Wait for thread 2 to start to increase chance of race */
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}
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printf("1: Unlocking to start increment loop %p\n", pthread_self());
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#endif
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PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
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while (count--) {
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PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
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#ifdef __FreeBSD__
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global_x = increment(global_x);
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#else
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global_x++;
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#endif
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PTHREAD_REQUIRE(pthread_mutex_unlock(&mutex));
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}
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@ -197,7 +243,14 @@ ATF_TC_BODY(mutex2, tc)
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PTHREAD_REQUIRE(mutex_lock(&mutex, &ts_lengthy));
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printf("1: Thread joined. X was %d. Return value (long) was %ld\n",
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global_x, (long)joinval);
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#ifdef __FreeBSD__
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ATF_REQUIRE_EQ_MSG(count, -1, "%d", count);
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ATF_REQUIRE_EQ_MSG((long)joinval, -1, "%ld", (long)joinval);
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ATF_REQUIRE_EQ_MSG(global_x, num_increments * 2, "%d vs %d", global_x,
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num_increments * 2);
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#else
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ATF_REQUIRE_EQ(global_x, 20000000);
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#endif
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#ifdef __NetBSD__
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#if defined(__powerpc__)
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@ -210,16 +263,27 @@ ATF_TC_BODY(mutex2, tc)
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#endif
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}
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#ifdef __FreeBSD__
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static volatile bool thread3_started = false;
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#endif
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static void *
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mutex3_threadfunc(void *arg)
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{
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long count = *(int *)arg;
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#ifdef __FreeBSD__
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thread3_started = true;
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#endif
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printf("2: Second thread (%p). Count is %ld\n", pthread_self(), count);
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while (count--) {
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PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
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#ifdef __FreeBSD__
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global_x = increment(global_x);
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#else
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global_x++;
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#endif
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PTHREAD_REQUIRE(pthread_mutex_unlock(&static_mutex));
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}
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@ -236,16 +300,13 @@ ATF_TC_HEAD(mutex3, tc)
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atf_tc_set_md_var(tc, "timeout", "40");
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#endif
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#endif
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#ifdef __FreeBSD__
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#if defined(__riscv)
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atf_tc_set_md_var(tc, "timeout", "600");
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#endif
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#endif
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}
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ATF_TC_BODY(mutex3, tc)
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{
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int count, count2;
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#ifdef __FreeBSD__
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int num_increments;
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#endif
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pthread_t new;
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void *joinval;
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@ -258,18 +319,36 @@ ATF_TC_BODY(mutex3, tc)
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#endif
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global_x = 0;
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#ifdef __FreeBSD__
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num_increments = count = count2 = 1000;
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if (getenv("NUM_ITERATIONS") != NULL) {
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num_increments = count = count2 =
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MIN(INT_MAX, strtoul(getenv("NUM_ITERATIONS"), NULL, 10));
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}
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printf("Will use %d iterations\n", num_increments);
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#else
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count = count2 = 10000000;
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#endif
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PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
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PTHREAD_REQUIRE(pthread_create(&new, NULL, mutex3_threadfunc, &count2));
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printf("1: Thread %p\n", pthread_self());
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#ifdef __FreeBSD__
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while (!thread3_started) {
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/* Wait for thread 3 to start to increase chance of race */
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}
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printf("1: Unlocking to start increment loop %p\n", pthread_self());
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#endif
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PTHREAD_REQUIRE(pthread_mutex_unlock(&static_mutex));
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while (count--) {
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PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
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#ifdef __FreeBSD__
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global_x = increment(global_x);
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#else
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global_x++;
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#endif
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PTHREAD_REQUIRE(pthread_mutex_unlock(&static_mutex));
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}
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@ -278,8 +357,14 @@ ATF_TC_BODY(mutex3, tc)
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PTHREAD_REQUIRE(mutex_lock(&static_mutex, &ts_lengthy));
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printf("1: Thread joined. X was %d. Return value (long) was %ld\n",
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global_x, (long)joinval);
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#ifdef __FreeBSD__
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ATF_REQUIRE_EQ_MSG(count, -1, "%d", count);
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ATF_REQUIRE_EQ_MSG((long)joinval, -1, "%ld", (long)joinval);
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ATF_REQUIRE_EQ_MSG(global_x, num_increments * 2, "%d vs %d", global_x,
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num_increments * 2);
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#else
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ATF_REQUIRE_EQ(global_x, 20000000);
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#endif
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#ifdef __NetBSD__
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#if defined(__powerpc__)
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/* XXX force a timeout in ppc case since an un-triggered race
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