selftests/powerpc/dscr: Add lockstep test cases to DSCR explicit tests

Add new cases to the relevant tests that use explicitly synchronized
threads to test the behaviour across context switches with less
randomness. By locking the participants to the same CPU we guarantee a
context switch occurs each time they make progress, which is a likely
failure point if the kernel is not tracking the thread local DSCR
correctly.

The random case is left in to keep exercising potential edge cases.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-5-bgray@linux.ibm.com

3 files changed, 159 insertions, 14 deletions

diff --git a/tools/testing/selftests/powerpc/dscr/Makefile b/tools/testing/selftests/powerpc/dscr/Makefile
index 845db6273a1b..b29a8863a734 100644
--- a/tools/testing/selftests/powerpc/dscr/Makefile
+++ b/tools/testing/selftests/powerpc/dscr/Makefile
@@ -9,5 +9,6 @@ top_srcdir = ../../../../..
 include ../../lib.mk
 
 $(OUTPUT)/dscr_default_test: LDLIBS += -lpthread
+$(OUTPUT)/dscr_explicit_test: LDLIBS += -lpthread
 
 $(TEST_GEN_PROGS): ../harness.c ../utils.c
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
index e76611e608af..18e533d46c9a 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_default_test.c
@@ -9,8 +9,66 @@
  * Copyright 2012, Anton Blanchard, IBM Corporation.
  * Copyright 2015, Anshuman Khandual, IBM Corporation.
  */
+
+#define _GNU_SOURCE
+
 #include "dscr.h"
 
+#include <pthread.h>
+#include <semaphore.h>
+#include <unistd.h>
+
+static void *dscr_default_lockstep_writer(void *arg)
+{
+	sem_t *reader_sem = (sem_t *)arg;
+	sem_t *writer_sem = (sem_t *)arg + 1;
+	unsigned long expected_dscr = 0;
+
+	for (int i = 0; i < COUNT; i++) {
+		FAIL_IF_EXIT(sem_wait(writer_sem));
+
+		set_default_dscr(expected_dscr);
+		expected_dscr = (expected_dscr + 1) % DSCR_MAX;
+
+		FAIL_IF_EXIT(sem_post(reader_sem));
+	}
+
+	return NULL;
+}
+
+int dscr_default_lockstep_test(void)
+{
+	pthread_t writer;
+	sem_t rw_semaphores[2];
+	sem_t *reader_sem = &rw_semaphores[0];
+	sem_t *writer_sem = &rw_semaphores[1];
+	unsigned long expected_dscr = 0;
+
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
+
+	FAIL_IF(sem_init(reader_sem, 0, 0));
+	FAIL_IF(sem_init(writer_sem, 0, 1));  /* writer starts first */
+	FAIL_IF(bind_to_cpu(BIND_CPU_ANY) < 0);
+	FAIL_IF(pthread_create(&writer, NULL, dscr_default_lockstep_writer, (void *)rw_semaphores));
+
+	for (int i = 0; i < COUNT ; i++) {
+		FAIL_IF(sem_wait(reader_sem));
+
+		FAIL_IF(get_dscr() != expected_dscr);
+		FAIL_IF(get_dscr_usr() != expected_dscr);
+
+		expected_dscr = (expected_dscr + 1) % DSCR_MAX;
+
+		FAIL_IF(sem_post(writer_sem));
+	}
+
+	FAIL_IF(pthread_join(writer, NULL));
+	FAIL_IF(sem_destroy(reader_sem));
+	FAIL_IF(sem_destroy(writer_sem));
+
+	return 0;
+}
+
 static unsigned long dscr;		/* System DSCR default */
 static unsigned long sequence;
 static unsigned long result[THREADS];
@@ -57,16 +115,13 @@ static void *do_test(void *in)
 	pthread_exit(&result[thread]);
 }
 
-int dscr_default(void)
+int dscr_default_random_test(void)
 {
 	pthread_t threads[THREADS];
 	unsigned long i, *status[THREADS];
-	unsigned long orig_dscr_default;
 
 	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
 
-	orig_dscr_default = get_default_dscr();
-
 	/* Initial DSCR default */
 	dscr = 1;
 	set_default_dscr(dscr);
@@ -75,7 +130,7 @@ int dscr_default(void)
 	for (i = 0; i < THREADS; i++) {
 		if (pthread_create(&threads[i], NULL, do_test, (void *)i)) {
 			perror("pthread_create() failed");
-			goto fail;
+			return 1;
 		}
 	}
 
@@ -104,23 +159,31 @@ int dscr_default(void)
 	for (i = 0; i < THREADS; i++) {
 		if (pthread_join(threads[i], (void **)&(status[i]))) {
 			perror("pthread_join() failed");
-			goto fail;
+			return 1;
 		}
 
 		if (*status[i]) {
 			printf("%ldth thread failed to join with %ld status\n",
 								i, *status[i]);
-			goto fail;
+			return 1;
 		}
 	}
-	set_default_dscr(orig_dscr_default);
 	return 0;
-fail:
-	set_default_dscr(orig_dscr_default);
-	return 1;
 }
 
 int main(int argc, char *argv[])
 {
-	return test_harness(dscr_default, "dscr_default_test");
+	unsigned long orig_dscr_default = 0;
+	int err = 0;
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		orig_dscr_default = get_default_dscr();
+
+	err |= test_harness(dscr_default_lockstep_test, "dscr_default_lockstep_test");
+	err |= test_harness(dscr_default_random_test, "dscr_default_random_test");
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		set_default_dscr(orig_dscr_default);
+
+	return err;
 }
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
index 5659d98cf340..3b98b9a88207 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
+++ b/tools/testing/selftests/powerpc/dscr/dscr_explicit_test.c
@@ -15,9 +15,78 @@
  * Copyright 2012, Anton Blanchard, IBM Corporation.
  * Copyright 2015, Anshuman Khandual, IBM Corporation.
  */
+
+#define _GNU_SOURCE
+
 #include "dscr.h"
+#include "utils.h"
+
+#include <pthread.h>
+#include <sched.h>
+#include <semaphore.h>
+
+void *dscr_explicit_lockstep_thread(void *args)
+{
+	sem_t *prev = (sem_t *)args;
+	sem_t *next = (sem_t *)args + 1;
+	unsigned long expected_dscr = 0;
+
+	set_dscr(expected_dscr);
+	srand(gettid());
+
+	for (int i = 0; i < COUNT; i++) {
+		FAIL_IF_EXIT(sem_wait(prev));
+
+		FAIL_IF_EXIT(expected_dscr != get_dscr());
+		FAIL_IF_EXIT(expected_dscr != get_dscr_usr());
+
+		expected_dscr = (expected_dscr + 1) % DSCR_MAX;
+		set_dscr(expected_dscr);
+
+		FAIL_IF_EXIT(sem_post(next));
+	}
+
+	return NULL;
+}
+
+int dscr_explicit_lockstep_test(void)
+{
+	pthread_t thread;
+	sem_t semaphores[2];
+	sem_t *prev = &semaphores[1];  /* reversed prev/next than for the other thread */
+	sem_t *next = &semaphores[0];
+	unsigned long expected_dscr = 0;
+
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_DSCR));
+
+	srand(gettid());
+	set_dscr(expected_dscr);
+
+	FAIL_IF(sem_init(prev, 0, 0));
+	FAIL_IF(sem_init(next, 0, 1));  /* other thread starts first */
+	FAIL_IF(bind_to_cpu(BIND_CPU_ANY) < 0);
+	FAIL_IF(pthread_create(&thread, NULL, dscr_explicit_lockstep_thread, (void *)semaphores));
+
+	for (int i = 0; i < COUNT; i++) {
+		FAIL_IF(sem_wait(prev));
+
+		FAIL_IF(expected_dscr != get_dscr());
+		FAIL_IF(expected_dscr != get_dscr_usr());
+
+		expected_dscr = (expected_dscr - 1) % DSCR_MAX;
+		set_dscr(expected_dscr);
+
+		FAIL_IF(sem_post(next));
+	}
 
-int dscr_explicit(void)
+	FAIL_IF(pthread_join(thread, NULL));
+	FAIL_IF(sem_destroy(prev));
+	FAIL_IF(sem_destroy(next));
+
+	return 0;
+}
+
+int dscr_explicit_random_test(void)
 {
 	unsigned long i, dscr = 0;
 
@@ -66,5 +135,17 @@ int dscr_explicit(void)
 
 int main(int argc, char *argv[])
 {
-	return test_harness(dscr_explicit, "dscr_explicit_test");
+	unsigned long orig_dscr_default = 0;
+	int err = 0;
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		orig_dscr_default = get_default_dscr();
+
+	err |= test_harness(dscr_explicit_lockstep_test, "dscr_explicit_lockstep_test");
+	err |= test_harness(dscr_explicit_random_test, "dscr_explicit_random_test");
+
+	if (have_hwcap2(PPC_FEATURE2_DSCR))
+		set_default_dscr(orig_dscr_default);
+
+	return err;
 }