[RFC,v2,7/8] selftests/perf: Add kselftest for process-wide sigtrap handling

diff --git a/tools/testing/selftests/perf_events/.gitignore b/tools/testing/selftests/perf_events/.gitignore
new file mode 100644
index 000000000000..4dc43e1bd79c
--- /dev/null
+++ b/tools/testing/selftests/perf_events/.gitignore
@@ -0,0 +1,2 @@ 
+# SPDX-License-Identifier: GPL-2.0-only
+sigtrap_threads
diff --git a/tools/testing/selftests/perf_events/Makefile b/tools/testing/selftests/perf_events/Makefile
new file mode 100644
index 000000000000..973a2c39ca83
--- /dev/null
+++ b/tools/testing/selftests/perf_events/Makefile
@@ -0,0 +1,6 @@ 
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -Wl,-no-as-needed -Wall -I../../../../usr/include
+LDFLAGS += -lpthread
+
+TEST_GEN_PROGS := sigtrap_threads
+include ../lib.mk
diff --git a/tools/testing/selftests/perf_events/config b/tools/testing/selftests/perf_events/config
new file mode 100644
index 000000000000..ba58ff2203e4
--- /dev/null
+++ b/tools/testing/selftests/perf_events/config
@@ -0,0 +1 @@ 
+CONFIG_PERF_EVENTS=y
diff --git a/tools/testing/selftests/perf_events/settings b/tools/testing/selftests/perf_events/settings
new file mode 100644
index 000000000000..6091b45d226b
--- /dev/null
+++ b/tools/testing/selftests/perf_events/settings
@@ -0,0 +1 @@ 
+timeout=120
diff --git a/tools/testing/selftests/perf_events/sigtrap_threads.c b/tools/testing/selftests/perf_events/sigtrap_threads.c
new file mode 100644
index 000000000000..7ebb9bb34c2e
--- /dev/null
+++ b/tools/testing/selftests/perf_events/sigtrap_threads.c
@@ -0,0 +1,202 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test for perf events with SIGTRAP across all threads.
+ *
+ * Copyright (C) 2021, Google LLC.
+ */
+
+#define _GNU_SOURCE
+#include <sys/types.h>
+
+/* We need the latest siginfo from the kernel repo. */
+#include <asm/siginfo.h>
+#define __have_siginfo_t 1
+#define __have_sigval_t 1
+#define __have_sigevent_t 1
+
+#include <linux/hw_breakpoint.h>
+#include <linux/perf_event.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdatomic.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "../kselftest_harness.h"
+
+#define NUM_THREADS 5
+
+/* 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. */
+	siginfo_t first_siginfo;	/* First observed siginfo_t. */
+} ctx;
+
+static struct perf_event_attr make_event_attr(bool enabled, volatile void *addr)
+{
+	struct perf_event_attr attr = {
+		.type		= PERF_TYPE_BREAKPOINT,
+		.size		= sizeof(attr),
+		.sample_period	= 1,
+		.disabled	= !enabled,
+		.bp_addr	= (long)addr,
+		.bp_type	= HW_BREAKPOINT_RW,
+		.bp_len		= HW_BREAKPOINT_LEN_1,
+		.inherit	= 1, /* Children inherit events ... */
+		.inherit_thread = 1, /* ... but only cloned with CLONE_THREAD. */
+		.remove_on_exec = 1, /* Required by sigtrap. */
+		.sigtrap	= 1, /* Request synchronous SIGTRAP on event. */
+	};
+	return attr;
+}
+
+static void sigtrap_handler(int signum, siginfo_t *info, void *ucontext)
+{
+	if (info->si_code != TRAP_PERF) {
+		fprintf(stderr, "%s: unexpected si_code %d\n", __func__, info->si_code);
+		return;
+	}
+
+	/*
+	 * The data in siginfo_t we're interested in should all be the same
+	 * across threads.
+	 */
+	if (!__atomic_fetch_add(&ctx.signal_count, 1, __ATOMIC_RELAXED))
+		ctx.first_siginfo = *info;
+	__atomic_fetch_sub(&ctx.tids_want_signal, syscall(__NR_gettid), __ATOMIC_RELAXED);
+}
+
+static void *test_thread(void *arg)
+{
+	pthread_barrier_t *barrier = (pthread_barrier_t *)arg;
+	pid_t tid = syscall(__NR_gettid);
+	int iter;
+	int i;
+
+	pthread_barrier_wait(barrier);
+
+	__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 */
+	}
+
+	return NULL;
+}
+
+FIXTURE(sigtrap_threads)
+{
+	struct sigaction oldact;
+	pthread_t threads[NUM_THREADS];
+	pthread_barrier_t barrier;
+	int fd;
+};
+
+FIXTURE_SETUP(sigtrap_threads)
+{
+	struct perf_event_attr attr = make_event_attr(false, &ctx.iterate_on);
+	struct sigaction action = {};
+	int i;
+
+	memset(&ctx, 0, sizeof(ctx));
+
+	/* Initialize sigtrap handler. */
+	action.sa_flags = SA_SIGINFO | SA_NODEFER;
+	action.sa_sigaction = sigtrap_handler;
+	sigemptyset(&action.sa_mask);
+	ASSERT_EQ(sigaction(SIGTRAP, &action, &self->oldact), 0);
+
+	/* Initialize perf event. */
+	self->fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, PERF_FLAG_FD_CLOEXEC);
+	ASSERT_NE(self->fd, -1);
+
+	/* Spawn threads inheriting perf event. */
+	pthread_barrier_init(&self->barrier, NULL, NUM_THREADS + 1);
+	for (i = 0; i < NUM_THREADS; i++)
+		ASSERT_EQ(pthread_create(&self->threads[i], NULL, test_thread, &self->barrier), 0);
+}
+
+FIXTURE_TEARDOWN(sigtrap_threads)
+{
+	pthread_barrier_destroy(&self->barrier);
+	close(self->fd);
+	sigaction(SIGTRAP, &self->oldact, NULL);
+}
+
+static void run_test_threads(struct __test_metadata *_metadata,
+			     FIXTURE_DATA(sigtrap_threads) *self)
+{
+	int i;
+
+	pthread_barrier_wait(&self->barrier);
+	for (i = 0; i < NUM_THREADS; i++)
+		ASSERT_EQ(pthread_join(self->threads[i], NULL), 0);
+}
+
+TEST_F(sigtrap_threads, remain_disabled)
+{
+	run_test_threads(_metadata, self);
+	EXPECT_EQ(ctx.signal_count, 0);
+	EXPECT_NE(ctx.tids_want_signal, 0);
+}
+
+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(ctx.first_siginfo.si_addr, &ctx.iterate_on);
+	EXPECT_EQ(ctx.first_siginfo.si_errno, PERF_TYPE_BREAKPOINT);
+	EXPECT_EQ(ctx.first_siginfo.si_perf, (HW_BREAKPOINT_LEN_1 << 16) | HW_BREAKPOINT_RW);
+
+	/* Check enabled for parent. */
+	ctx.iterate_on = 0;
+	EXPECT_EQ(ctx.signal_count, NUM_THREADS + 1);
+}
+
+/* Test that modification propagates to all inherited events. */
+TEST_F(sigtrap_threads, modify_and_enable_event)
+{
+	struct perf_event_attr new_attr = make_event_attr(true, &ctx.iterate_on);
+
+	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(ctx.first_siginfo.si_addr, &ctx.iterate_on);
+	EXPECT_EQ(ctx.first_siginfo.si_errno, PERF_TYPE_BREAKPOINT);
+	EXPECT_EQ(ctx.first_siginfo.si_perf, (HW_BREAKPOINT_LEN_1 << 16) | HW_BREAKPOINT_RW);
+
+	/* Check enabled for parent. */
+	ctx.iterate_on = 0;
+	EXPECT_EQ(ctx.signal_count, NUM_THREADS + 1);
+}
+
+/* Stress test event + signal handling. */
+TEST_F(sigtrap_threads, signal_stress)
+{
+	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(ctx.first_siginfo.si_addr, &ctx.iterate_on);
+	EXPECT_EQ(ctx.first_siginfo.si_errno, PERF_TYPE_BREAKPOINT);
+	EXPECT_EQ(ctx.first_siginfo.si_perf, (HW_BREAKPOINT_LEN_1 << 16) | HW_BREAKPOINT_RW);
+}
+
+TEST_HARNESS_MAIN