selftests/perf_events: Add kselftest for remove_on_exec

Add kselftest to test that remove_on_exec removes inherited events from
child tasks.

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

tools/testing/selftests/perf_events/.gitignore

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 # SPDX-License-Identifier: GPL-2.0-only
 sigtrap_threads
+remove_on_exec

tools/testing/selftests/perf_events/Makefile

···
 CFLAGS += -Wl,-no-as-needed -Wall -I../../../../usr/include
 LDFLAGS += -lpthread
 
-TEST_GEN_PROGS := sigtrap_threads
+TEST_GEN_PROGS := sigtrap_threads remove_on_exec
 include ../lib.mk

tools/testing/selftests/perf_events/remove_on_exec.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test for remove_on_exec.
+ *
+ * Copyright (C) 2021, Google LLC.
+ */
+
+#define _GNU_SOURCE
+
+/* We need the latest siginfo from the kernel repo. */
+#include <sys/types.h>
+#include <asm/siginfo.h>
+#define __have_siginfo_t 1
+#define __have_sigval_t 1
+#define __have_sigevent_t 1
+#define __siginfo_t_defined
+#define __sigval_t_defined
+#define __sigevent_t_defined
+#define _BITS_SIGINFO_CONSTS_H 1
+#define _BITS_SIGEVENT_CONSTS_H 1
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <linux/perf_event.h>
+#include <pthread.h>
+#include <signal.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "../kselftest_harness.h"
+
+static volatile int signal_count;
+
+static struct perf_event_attr make_event_attr(void)
+{
+	struct perf_event_attr attr = {
+		.type		= PERF_TYPE_HARDWARE,
+		.size		= sizeof(attr),
+		.config		= PERF_COUNT_HW_INSTRUCTIONS,
+		.sample_period	= 1000,
+		.exclude_kernel = 1,
+		.exclude_hv	= 1,
+		.disabled	= 1,
+		.inherit	= 1,
+		/*
+		 * Children normally retain their inherited event on exec; with
+		 * remove_on_exec, we'll remove their event, but the parent and
+		 * any other non-exec'd children will keep their events.
+		 */
+		.remove_on_exec = 1,
+		.sigtrap	= 1,
+	};
+	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;
+	}
+
+	signal_count++;
+}
+
+FIXTURE(remove_on_exec)
+{
+	struct sigaction oldact;
+	int fd;
+};
+
+FIXTURE_SETUP(remove_on_exec)
+{
+	struct perf_event_attr attr = make_event_attr();
+	struct sigaction action = {};
+
+	signal_count = 0;
+
+	/* 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);
+}
+
+FIXTURE_TEARDOWN(remove_on_exec)
+{
+	close(self->fd);
+	sigaction(SIGTRAP, &self->oldact, NULL);
+}
+
+/* Verify event propagates to fork'd child. */
+TEST_F(remove_on_exec, fork_only)
+{
+	int status;
+	pid_t pid = fork();
+
+	if (pid == 0) {
+		ASSERT_EQ(signal_count, 0);
+		ASSERT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
+		while (!signal_count);
+		_exit(42);
+	}
+
+	while (!signal_count); /* Child enables event. */
+	EXPECT_EQ(waitpid(pid, &status, 0), pid);
+	EXPECT_EQ(WEXITSTATUS(status), 42);
+}
+
+/*
+ * Verify that event does _not_ propagate to fork+exec'd child; event enabled
+ * after fork+exec.
+ */
+TEST_F(remove_on_exec, fork_exec_then_enable)
+{
+	pid_t pid_exec, pid_only_fork;
+	int pipefd[2];
+	int tmp;
+
+	/*
+	 * Non-exec child, to ensure exec does not affect inherited events of
+	 * other children.
+	 */
+	pid_only_fork = fork();
+	if (pid_only_fork == 0) {
+		/* Block until parent enables event. */
+		while (!signal_count);
+		_exit(42);
+	}
+
+	ASSERT_NE(pipe(pipefd), -1);
+	pid_exec = fork();
+	if (pid_exec == 0) {
+		ASSERT_NE(dup2(pipefd[1], STDOUT_FILENO), -1);
+		close(pipefd[0]);
+		execl("/proc/self/exe", "exec_child", NULL);
+		_exit((perror("exec failed"), 1));
+	}
+	close(pipefd[1]);
+
+	ASSERT_EQ(waitpid(pid_exec, &tmp, WNOHANG), 0); /* Child is running. */
+	/* Wait for exec'd child to start spinning. */
+	EXPECT_EQ(read(pipefd[0], &tmp, sizeof(int)), sizeof(int));
+	EXPECT_EQ(tmp, 42);
+	close(pipefd[0]);
+	/* Now we can enable the event, knowing the child is doing work. */
+	EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
+	/* If the event propagated to the exec'd child, it will exit normally... */
+	usleep(100000); /* ... give time for event to trigger (in case of bug). */
+	EXPECT_EQ(waitpid(pid_exec, &tmp, WNOHANG), 0); /* Should still be running. */
+	EXPECT_EQ(kill(pid_exec, SIGKILL), 0);
+
+	/* Verify removal from child did not affect this task's event. */
+	tmp = signal_count;
+	while (signal_count == tmp); /* Should not hang! */
+	/* Nor should it have affected the first child. */
+	EXPECT_EQ(waitpid(pid_only_fork, &tmp, 0), pid_only_fork);
+	EXPECT_EQ(WEXITSTATUS(tmp), 42);
+}
+
+/*
+ * Verify that event does _not_ propagate to fork+exec'd child; event enabled
+ * before fork+exec.
+ */
+TEST_F(remove_on_exec, enable_then_fork_exec)
+{
+	pid_t pid_exec;
+	int tmp;
+
+	EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
+
+	pid_exec = fork();
+	if (pid_exec == 0) {
+		execl("/proc/self/exe", "exec_child", NULL);
+		_exit((perror("exec failed"), 1));
+	}
+
+	/*
+	 * The child may exit abnormally at any time if the event propagated and
+	 * a SIGTRAP is sent before the handler was set up.
+	 */
+	usleep(100000); /* ... give time for event to trigger (in case of bug). */
+	EXPECT_EQ(waitpid(pid_exec, &tmp, WNOHANG), 0); /* Should still be running. */
+	EXPECT_EQ(kill(pid_exec, SIGKILL), 0);
+
+	/* Verify removal from child did not affect this task's event. */
+	tmp = signal_count;
+	while (signal_count == tmp); /* Should not hang! */
+}
+
+TEST_F(remove_on_exec, exec_stress)
+{
+	pid_t pids[30];
+	int i, tmp;
+
+	for (i = 0; i < sizeof(pids) / sizeof(pids[0]); i++) {
+		pids[i] = fork();
+		if (pids[i] == 0) {
+			execl("/proc/self/exe", "exec_child", NULL);
+			_exit((perror("exec failed"), 1));
+		}
+
+		/* Some forked with event disabled, rest with enabled. */
+		if (i > 10)
+			EXPECT_EQ(ioctl(self->fd, PERF_EVENT_IOC_ENABLE, 0), 0);
+	}
+
+	usleep(100000); /* ... give time for event to trigger (in case of bug). */
+
+	for (i = 0; i < sizeof(pids) / sizeof(pids[0]); i++) {
+		/* All children should still be running. */
+		EXPECT_EQ(waitpid(pids[i], &tmp, WNOHANG), 0);
+		EXPECT_EQ(kill(pids[i], SIGKILL), 0);
+	}
+
+	/* Verify event is still alive. */
+	tmp = signal_count;
+	while (signal_count == tmp);
+}
+
+/* For exec'd child. */
+static void exec_child(void)
+{
+	struct sigaction action = {};
+	const int val = 42;
+
+	/* Set up sigtrap handler in case we erroneously receive a trap. */
+	action.sa_flags = SA_SIGINFO | SA_NODEFER;
+	action.sa_sigaction = sigtrap_handler;
+	sigemptyset(&action.sa_mask);
+	if (sigaction(SIGTRAP, &action, NULL))
+		_exit((perror("sigaction failed"), 1));
+
+	/* Signal parent that we're starting to spin. */
+	if (write(STDOUT_FILENO, &val, sizeof(int)) == -1)
+		_exit((perror("write failed"), 1));
+
+	/* Should hang here until killed. */
+	while (!signal_count);
+}
+
+#define main test_main
+TEST_HARNESS_MAIN
+#undef main
+int main(int argc, char *argv[])
+{
+	if (!strcmp(argv[0], "exec_child")) {
+		exec_child();
+		return 1;
+	}
+
+	return test_main(argc, argv);
+}