selftests/perf_events: Add a SIGTRAP stress test with disables

Add a SIGTRAP stress test that exercises repeatedly enabling/disabling
an event while it concurrently keeps firing.

Signed-off-by: Marco Elver <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]/

tools/testing/selftests/perf_events/sigtrap_threads.c

···
 		.remove_on_exec = 1, /* Required by sigtrap. */
 		.sigtrap	= 1, /* Request synchronous SIGTRAP on event. */
 		.sig_data	= TEST_SIG_DATA(addr, id),
+		.exclude_kernel = 1, /* To allow */
+		.exclude_hv     = 1, /* running as !root */
 	};
 	return attr;
 }
···
 
 	__atomic_fetch_add(&ctx.tids_want_signal, tid, __ATOMIC_RELAXED);
 	iter = ctx.iterate_on; /* read */
-	for (i = 0; i < iter - 1; i++) {
-		__atomic_fetch_add(&ctx.tids_want_signal, tid, __ATOMIC_RELAXED);
-		ctx.iterate_on = iter; /* idempotent write */
+	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 */
+		}
+	} else {
+		while (ctx.iterate_on);
 	}
 
 	return NULL;
···
 
 	EXPECT_EQ(ctx.signal_count, NUM_THREADS * ctx.iterate_on);
 	EXPECT_EQ(ctx.tids_want_signal, 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));
+}
+
+TEST_F(sigtrap_threads, signal_stress_with_disable)
+{
+	const int target_count = NUM_THREADS * 3000;
+	int i;
+
+	ctx.iterate_on = -1;
+
+	EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
+	pthread_barrier_wait(&self->barrier);
+	while (__atomic_load_n(&ctx.signal_count, __ATOMIC_RELAXED) < target_count) {
+		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;
+	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);
+
 	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));