Merge branch 'selftests-bpf-fix-for-bpf_signal-stalls-watchdog-for-test_progs'

Eduard Zingerman says:

====================
selftests/bpf: fix for bpf_signal stalls, watchdog for test_progs

Test case 'bpf_signal' had been recently reported to stall, both on
the mailing list [1] and CI [2]. The stall is caused by CPU cycles
perf event not being delivered within expected time frame, before test
process enters system call and waits indefinitely.

This patch-set addresses the issue in several ways:
- A watchdog timer is added to test_progs.c runner:
  - it prints current sub-test name to stderr if sub-test takes longer
    than 10 seconds to finish;
  - it terminates process executing sub-test if sub-test takes longer
    than 120 seconds to finish.
- The test case is updated to await perf event notification with a
  timeout and a few retries, this serves two purposes:
  - busy loops longer to increase the time frame for CPU cycles event
    generation/delivery;
  - makes a timeout, not stall, a worst case scenario.
- The test case is updated to lower frequency of perf events, as high
  frequency of such events caused events generation throttling,
  which in turn delayed events delivery by amount of time sufficient
  to cause test case failure.

Note:

  librt pthread-based timer API is used to implement watchdog timer.
  I chose this API over SIGALRM because signal handler execution
  within test process context was sufficient to trigger perf event
  delivery for send_signal/send_signal_nmi_thread_remote test case,
  w/o any additional changes. Thus I concluded that SIGALRM based
  implementation interferes with tests execution.

[1] https://lore.kernel.org/bpf/CAP01T75OUeE8E-Lw9df84dm8ag2YmHW619f1DmPSVZ5_O89+Bg@mail.gmail.com/
[2] https://github.com/kernel-patches/bpf/actions/runs/11791485271/job/32843996871
====================

Link: https://lore.kernel.org/r/20241112110906.3045278-1-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -742,6 +742,7 @@ TRUNNER_EXTRA_SOURCES := test_progs.c		\
 			 unpriv_helpers.c 	\
 			 netlink_helpers.c	\
 			 jit_disasm_helpers.c	\
+			 io_helpers.c		\
 			 test_loader.c		\
 			 xsk.c			\
 			 disasm.c		\

tools/testing/selftests/bpf/io_helpers.c

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <sys/select.h>
+#include <unistd.h>
+#include <errno.h>
+
+int read_with_timeout(int fd, char *buf, size_t count, long usec)
+{
+	const long M = 1000 * 1000;
+	struct timeval tv = { usec / M, usec % M };
+	fd_set fds;
+	int err;
+
+	FD_ZERO(&fds);
+	FD_SET(fd, &fds);
+	err = select(fd + 1, &fds, NULL, NULL, &tv);
+	if (err < 0)
+		return err;
+	if (FD_ISSET(fd, &fds))
+		return read(fd, buf, count);
+	return -EAGAIN;
+}

tools/testing/selftests/bpf/io_helpers.h

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <unistd.h>
+
+/* As a regular read(2), but allows to specify a timeout in micro-seconds.
+ * Returns -EAGAIN on timeout.
+ */
+int read_with_timeout(int fd, char *buf, size_t count, long usec);

tools/testing/selftests/bpf/prog_tests/bpf_iter.c

@@ -265,10 +265,10 @@ static void *run_test_task_tid(void *arg)
 
 	linfo.task.tid = 0;
 	linfo.task.pid = getpid();
-	/* This includes the parent thread, this thread,
+	/* This includes the parent thread, this thread, watchdog timer thread
 	 * and the do_nothing_wait thread
 	 */
-	test_task_common(&opts, 2, 1);
+	test_task_common(&opts, 3, 1);
 
 	test_task_common_nocheck(NULL, &num_unknown_tid, &num_known_tid);
 	ASSERT_GT(num_unknown_tid, 2, "check_num_unknown_tid");
@@ -297,7 +297,7 @@ static void test_task_pid(void)
 	opts.link_info = &linfo;
 	opts.link_info_len = sizeof(linfo);
 
-	test_task_common(&opts, 1, 1);
+	test_task_common(&opts, 2, 1);
 }
 
 static void test_task_pidfd(void)
@@ -315,7 +315,7 @@ static void test_task_pidfd(void)
 	opts.link_info = &linfo;
 	opts.link_info_len = sizeof(linfo);
 
-	test_task_common(&opts, 1, 1);
+	test_task_common(&opts, 2, 1);
 
 	close(pidfd);
 }

tools/testing/selftests/bpf/prog_tests/iters.c

@@ -192,8 +192,8 @@ static void subtest_task_iters(void)
 	syscall(SYS_getpgid);
 	iters_task__detach(skel);
 	ASSERT_EQ(skel->bss->procs_cnt, 1, "procs_cnt");
-	ASSERT_EQ(skel->bss->threads_cnt, thread_num + 1, "threads_cnt");
-	ASSERT_EQ(skel->bss->proc_threads_cnt, thread_num + 1, "proc_threads_cnt");
+	ASSERT_EQ(skel->bss->threads_cnt, thread_num + 2, "threads_cnt");
+	ASSERT_EQ(skel->bss->proc_threads_cnt, thread_num + 2, "proc_threads_cnt");
 	ASSERT_EQ(skel->bss->invalid_cnt, 0, "invalid_cnt");
 	pthread_mutex_unlock(&do_nothing_mutex);
 	for (int i = 0; i < thread_num; i++)

tools/testing/selftests/bpf/prog_tests/send_signal.c

@@ -3,6 +3,7 @@
 #include <sys/time.h>
 #include <sys/resource.h>
 #include "test_send_signal_kern.skel.h"
+#include "io_helpers.h"
 
 static int sigusr1_received;
 
@@ -24,6 +25,7 @@ static void test_send_signal_common(struct perf_event_attr *attr,
 	int pipe_c2p[2], pipe_p2c[2];
 	int err = -1, pmu_fd = -1;
 	volatile int j = 0;
+	int retry_count;
 	char buf[256];
 	pid_t pid;
 	int old_prio;
@@ -163,21 +165,25 @@ static void test_send_signal_common(struct perf_event_attr *attr,
 	/* notify child that bpf program can send_signal now */
 	ASSERT_EQ(write(pipe_p2c[1], buf, 1), 1, "pipe_write");
 
-	/* For the remote test, the BPF program is triggered from this
-	 * process but the other process/thread is signaled.
-	 */
-	if (remote) {
-		if (!attr) {
-			for (int i = 0; i < 10; i++)
-				usleep(1);
-		} else {
-			for (int i = 0; i < 100000000; i++)
-				j /= i + 1;
+	for (retry_count = 0;;) {
+		/* For the remote test, the BPF program is triggered from this
+		 * process but the other process/thread is signaled.
+		 */
+		if (remote) {
+			if (!attr) {
+				for (int i = 0; i < 10; i++)
+					usleep(1);
+			} else {
+				for (int i = 0; i < 100000000; i++)
+					j /= i + 1;
+			}
 		}
+		/* wait for result */
+		err = read_with_timeout(pipe_c2p[0], buf, 1, 100);
+		if (err == -EAGAIN && retry_count++ < 10000)
+			continue;
+		break;
 	}
-
-	/* wait for result */
-	err = read(pipe_c2p[0], buf, 1);
 	if (!ASSERT_GE(err, 0, "reading pipe"))
 		goto disable_pmu;
 	if (!ASSERT_GT(err, 0, "reading pipe error: size 0")) {
@@ -223,7 +229,8 @@ static void test_send_signal_perf(bool signal_thread, bool remote)
 static void test_send_signal_nmi(bool signal_thread, bool remote)
 {
 	struct perf_event_attr attr = {
-		.sample_period = 1,
+		.freq = 1,
+		.sample_freq = 1000,
 		.type = PERF_TYPE_HARDWARE,
 		.config = PERF_COUNT_HW_CPU_CYCLES,
 	};

tools/testing/selftests/bpf/test_progs.c

@@ -16,6 +16,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <bpf/btf.h>
+#include <time.h>
 #include "json_writer.h"
 
 #include "network_helpers.h"
@@ -179,6 +180,88 @@ int usleep(useconds_t usec)
 	return syscall(__NR_nanosleep, &ts, NULL);
 }
 
+/* Watchdog timer is started by watchdog_start() and stopped by watchdog_stop().
+ * If timer is active for longer than env.secs_till_notify,
+ * it prints the name of the current test to the stderr.
+ * If timer is active for longer than env.secs_till_kill,
+ * it kills the thread executing the test by sending a SIGSEGV signal to it.
+ */
+static void watchdog_timer_func(union sigval sigval)
+{
+	struct itimerspec timeout = {};
+	char test_name[256];
+	int err;
+
+	if (env.subtest_state)
+		snprintf(test_name, sizeof(test_name), "%s/%s",
+			 env.test->test_name, env.subtest_state->name);
+	else
+		snprintf(test_name, sizeof(test_name), "%s",
+			 env.test->test_name);
+
+	switch (env.watchdog_state) {
+	case WD_NOTIFY:
+		fprintf(env.stderr_saved, "WATCHDOG: test case %s executes for %d seconds...\n",
+			test_name, env.secs_till_notify);
+		timeout.it_value.tv_sec = env.secs_till_kill - env.secs_till_notify;
+		env.watchdog_state = WD_KILL;
+		err = timer_settime(env.watchdog, 0, &timeout, NULL);
+		if (err)
+			fprintf(env.stderr_saved, "Failed to arm watchdog timer\n");
+		break;
+	case WD_KILL:
+		fprintf(env.stderr_saved,
+			"WATCHDOG: test case %s executes for %d seconds, terminating with SIGSEGV\n",
+			test_name, env.secs_till_kill);
+		pthread_kill(env.main_thread, SIGSEGV);
+		break;
+	}
+}
+
+static void watchdog_start(void)
+{
+	struct itimerspec timeout = {};
+	int err;
+
+	if (env.secs_till_kill == 0)
+		return;
+	if (env.secs_till_notify > 0) {
+		env.watchdog_state = WD_NOTIFY;
+		timeout.it_value.tv_sec = env.secs_till_notify;
+	} else {
+		env.watchdog_state = WD_KILL;
+		timeout.it_value.tv_sec = env.secs_till_kill;
+	}
+	err = timer_settime(env.watchdog, 0, &timeout, NULL);
+	if (err)
+		fprintf(env.stderr_saved, "Failed to start watchdog timer\n");
+}
+
+static void watchdog_stop(void)
+{
+	struct itimerspec timeout = {};
+	int err;
+
+	env.watchdog_state = WD_NOTIFY;
+	err = timer_settime(env.watchdog, 0, &timeout, NULL);
+	if (err)
+		fprintf(env.stderr_saved, "Failed to stop watchdog timer\n");
+}
+
+static void watchdog_init(void)
+{
+	struct sigevent watchdog_sev = {
+		.sigev_notify = SIGEV_THREAD,
+		.sigev_notify_function = watchdog_timer_func,
+	};
+	int err;
+
+	env.main_thread = pthread_self();
+	err = timer_create(CLOCK_MONOTONIC, &watchdog_sev, &env.watchdog);
+	if (err)
+		fprintf(stderr, "Failed to initialize watchdog timer\n");
+}
+
 static bool should_run(struct test_selector *sel, int num, const char *name)
 {
 	int i;
@@ -515,6 +598,7 @@ bool test__start_subtest(const char *subtest_name)
 
 	env.subtest_state = subtest_state;
 	stdio_hijack_init(&subtest_state->log_buf, &subtest_state->log_cnt);
+	watchdog_start();
 
 	return true;
 }
@@ -780,6 +864,7 @@ enum ARG_KEYS {
 	ARG_DEBUG = -1,
 	ARG_JSON_SUMMARY = 'J',
 	ARG_TRAFFIC_MONITOR = 'm',
+	ARG_WATCHDOG_TIMEOUT = 'w',
 };
 
 static const struct argp_option opts[] = {
@@ -810,6 +895,8 @@ static const struct argp_option opts[] = {
 	{ "traffic-monitor", ARG_TRAFFIC_MONITOR, "NAMES", 0,
 	  "Monitor network traffic of tests with name matching the pattern (supports '*' wildcard)." },
 #endif
+	{ "watchdog-timeout", ARG_WATCHDOG_TIMEOUT, "SECONDS", 0,
+	  "Kill the process if tests are not making progress for specified number of seconds." },
 	{},
 };
 
@@ -1035,6 +1122,16 @@ static error_t parse_arg(int key, char *arg, struct argp_state *state)
 					      true);
 		break;
 #endif
+	case ARG_WATCHDOG_TIMEOUT:
+		env->secs_till_kill = atoi(arg);
+		if (env->secs_till_kill < 0) {
+			fprintf(stderr, "Invalid watchdog timeout: %s.\n", arg);
+			return -EINVAL;
+		}
+		if (env->secs_till_kill < env->secs_till_notify) {
+			env->secs_till_notify = 0;
+		}
+		break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -1263,10 +1360,12 @@ static void run_one_test(int test_num)
 
 	stdio_hijack(&state->log_buf, &state->log_cnt);
 
+	watchdog_start();
 	if (test->run_test)
 		test->run_test();
 	else if (test->run_serial_test)
 		test->run_serial_test();
+	watchdog_stop();
 
 	/* ensure last sub-test is finalized properly */
 	if (env.subtest_state)
@@ -1707,6 +1806,7 @@ out:
 static int worker_main(int sock)
 {
 	save_netns();
+	watchdog_init();
 
 	while (true) {
 		/* receive command */
@@ -1816,6 +1916,8 @@ int main(int argc, char **argv)
 
 	sigaction(SIGSEGV, &sigact, NULL);
 
+	env.secs_till_notify = 10;
+	env.secs_till_kill = 120;
 	err = argp_parse(&argp, argc, argv, 0, NULL, &env);
 	if (err)
 		return err;
@@ -1824,6 +1926,8 @@ int main(int argc, char **argv)
 	if (err)
 		return err;
 
+	watchdog_init();
+
 	/* Use libbpf 1.0 API mode */
 	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
 	libbpf_set_print(libbpf_print_fn);

tools/testing/selftests/bpf/test_progs.h

@@ -131,6 +131,12 @@ struct test_env {
 	pid_t *worker_pids; /* array of worker pids */
 	int *worker_socks; /* array of worker socks */
 	int *worker_current_test; /* array of current running test for each worker */
+
+	pthread_t main_thread;
+	int secs_till_notify;
+	int secs_till_kill;
+	timer_t watchdog; /* watch for stalled tests/subtests */
+	enum { WD_NOTIFY, WD_KILL } watchdog_state;
 };
 
 #define MAX_LOG_TRUNK_SIZE 8192