[Devel] [PATCH] selftests/perf_events: fix sigtrap_threads tests fail with -O2
Eva Kurchatova
eva.kurchatova at virtuozzo.com
Fri May 8 15:39:31 MSK 2026
The enable_event and modify_and_enable_event tests fail when compiled
with -O2:
Expected ctx.signal_count (5) == NUM_THREADS + 1 (6)
The test sequence is:
EXPECT_EQ(ctx.signal_count, NUM_THREADS); /* compiler loads into reg */
ctx.iterate_on = 0; /* triggers SIGTRAP, handler
increments signal_count */
EXPECT_EQ(ctx.signal_count, NUM_THREADS + 1); /* stale cached value */
As SIGTRAP handler used atomics for signal_count and tids_want_signal,
test now correctly uses atomic access everywhere for those variables.
Additionally, use READ_ONCE/WRITE_ONCE macros for idempotent access to
iterate_on watchpoint and prevent reordering / misoptimization
https://virtuozzo.atlassian.net/browse/VSTOR-127669
Feature: fix selftests
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
---
.../selftests/perf_events/sigtrap_threads.c | 42 ++++++++++---------
1 file changed, 23 insertions(+), 19 deletions(-)
diff --git a/tools/testing/selftests/perf_events/sigtrap_threads.c b/tools/testing/selftests/perf_events/sigtrap_threads.c
index d1d8483ac628..ffc65d6f1c2b 100644
--- a/tools/testing/selftests/perf_events/sigtrap_threads.c
+++ b/tools/testing/selftests/perf_events/sigtrap_threads.c
@@ -35,11 +35,15 @@
#define NUM_THREADS 5
+/* Force watchpoint access to actually occur */
+#define READ_ONCE(x) (*(volatile typeof(x) *)&(x))
+#define WRITE_ONCE(x, val) (*(volatile typeof(x) *)&(x) = (val))
+
/* Data shared between test body, threads, and signal handler. */
static struct {
int tids_want_signal; /* Which threads still want a signal. */
int signal_count; /* Sanity check number of signals received. */
- volatile int iterate_on; /* Variable to set breakpoint on. */
+ int iterate_on; /* Variable to set breakpoint on. */
siginfo_t first_siginfo; /* First observed siginfo_t. */
} ctx;
@@ -94,14 +98,14 @@ static void *test_thread(void *arg)
pthread_barrier_wait(barrier);
__atomic_fetch_add(&ctx.tids_want_signal, tid, __ATOMIC_RELAXED);
- iter = ctx.iterate_on; /* read */
+ iter = READ_ONCE(ctx.iterate_on);
if (iter >= 0) {
for (i = 0; i < iter - 1; i++) {
__atomic_fetch_add(&ctx.tids_want_signal, tid, __ATOMIC_RELAXED);
- ctx.iterate_on = iter; /* idempotent write */
+ WRITE_ONCE(ctx.iterate_on, iter); /* idempotent write */
}
} else {
- while (ctx.iterate_on);
+ while (READ_ONCE(ctx.iterate_on));
}
return NULL;
@@ -159,8 +163,8 @@ static void run_test_threads(struct __test_metadata *_metadata,
TEST_F(sigtrap_threads, remain_disabled)
{
run_test_threads(_metadata, self);
- EXPECT_EQ(ctx.signal_count, 0);
- EXPECT_NE(ctx.tids_want_signal, 0);
+ EXPECT_EQ(__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED), 0);
+ EXPECT_NE(__atomic_load_n(&ctx.tids_want_signal, __ATOMIC_RELAXED), 0);
}
TEST_F(sigtrap_threads, enable_event)
@@ -168,15 +172,15 @@ TEST_F(sigtrap_threads, enable_event)
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
run_test_threads(_metadata, self);
- EXPECT_EQ(ctx.signal_count, NUM_THREADS);
- EXPECT_EQ(ctx.tids_want_signal, 0);
+ EXPECT_EQ(__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED), NUM_THREADS);
+ EXPECT_EQ(__atomic_load_n(&ctx.tids_want_signal, __ATOMIC_RELAXED), 0);
EXPECT_EQ(ctx.first_siginfo.si_addr, &ctx.iterate_on);
EXPECT_EQ(ctx.first_siginfo.si_perf_type, PERF_TYPE_BREAKPOINT);
EXPECT_EQ(ctx.first_siginfo.si_perf_data, TEST_SIG_DATA(&ctx.iterate_on, 0));
/* Check enabled for parent. */
- ctx.iterate_on = 0;
- EXPECT_EQ(ctx.signal_count, NUM_THREADS + 1);
+ WRITE_ONCE(ctx.iterate_on, 0);
+ EXPECT_EQ(__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED), NUM_THREADS + 1);
}
/* Test that modification propagates to all inherited events. */
@@ -187,28 +191,28 @@ TEST_F(sigtrap_threads, modify_and_enable_event)
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_MODIFY_ATTRIBUTES, &new_attr), 0);
run_test_threads(_metadata, self);
- EXPECT_EQ(ctx.signal_count, NUM_THREADS);
- EXPECT_EQ(ctx.tids_want_signal, 0);
+ EXPECT_EQ(__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED), NUM_THREADS);
+ EXPECT_EQ(__atomic_load_n(&ctx.tids_want_signal, __ATOMIC_RELAXED), 0);
EXPECT_EQ(ctx.first_siginfo.si_addr, &ctx.iterate_on);
EXPECT_EQ(ctx.first_siginfo.si_perf_type, PERF_TYPE_BREAKPOINT);
EXPECT_EQ(ctx.first_siginfo.si_perf_data, TEST_SIG_DATA(&ctx.iterate_on, 42));
/* Check enabled for parent. */
- ctx.iterate_on = 0;
- EXPECT_EQ(ctx.signal_count, NUM_THREADS + 1);
+ WRITE_ONCE(ctx.iterate_on, 0);
+ EXPECT_EQ(__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED), NUM_THREADS + 1);
}
/* Stress test event + signal handling. */
TEST_F(sigtrap_threads, signal_stress)
{
- ctx.iterate_on = 3000;
+ WRITE_ONCE(ctx.iterate_on, 3000);
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
run_test_threads(_metadata, self);
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_DISABLE, 0), 0);
- EXPECT_EQ(ctx.signal_count, NUM_THREADS * ctx.iterate_on);
- EXPECT_EQ(ctx.tids_want_signal, 0);
+ EXPECT_EQ(__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED), NUM_THREADS * READ_ONCE(ctx.iterate_on));
+ EXPECT_EQ(__atomic_load_n(&ctx.tids_want_signal, __ATOMIC_RELAXED), 0);
EXPECT_EQ(ctx.first_siginfo.si_addr, &ctx.iterate_on);
EXPECT_EQ(ctx.first_siginfo.si_perf_type, PERF_TYPE_BREAKPOINT);
EXPECT_EQ(ctx.first_siginfo.si_perf_data, TEST_SIG_DATA(&ctx.iterate_on, 0));
@@ -219,7 +223,7 @@ TEST_F(sigtrap_threads, signal_stress_with_disable)
const int target_count = NUM_THREADS * 3000;
int i;
- ctx.iterate_on = -1;
+ WRITE_ONCE(ctx.iterate_on, -1);
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
pthread_barrier_wait(&self->barrier);
@@ -227,7 +231,7 @@ TEST_F(sigtrap_threads, signal_stress_with_disable)
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_DISABLE, 0), 0);
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
}
- ctx.iterate_on = 0;
+ WRITE_ONCE(ctx.iterate_on, 0);
for (i = 0; i < NUM_THREADS; i++)
ASSERT_EQ(pthread_join(self->threads[i], NULL), 0);
EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_DISABLE, 0), 0);
--
2.54.0
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