[bpf-next 0/4] selftests/bpf: fix for bpf_signal stalls, watchdog for test_progs

[bpf-next 0/4] selftests/bpf: fix for bpf_signal stalls, watchdog for test_progs

[Eduard Zingerman]

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

Eduard Zingerman (4):
  selftests/bpf: watchdog timer for test_progs
  selftests/bpf: add read_with_timeout() utility function
  selftests/bpf: allow send_signal test to timeout
  selftests/bpf: update send_signal to lower perf evemts frequency

 tools/testing/selftests/bpf/Makefile          |   1 +
 tools/testing/selftests/bpf/io_helpers.c      |  21 ++++
 tools/testing/selftests/bpf/io_helpers.h      |   7 ++
 .../selftests/bpf/prog_tests/bpf_iter.c       |   8 +-
 .../testing/selftests/bpf/prog_tests/iters.c  |   4 +-
 .../selftests/bpf/prog_tests/send_signal.c    |  35 +++---
 tools/testing/selftests/bpf/test_progs.c      | 104 ++++++++++++++++++
 tools/testing/selftests/bpf/test_progs.h      |   6 +
 8 files changed, 166 insertions(+), 20 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/io_helpers.c
 create mode 100644 tools/testing/selftests/bpf/io_helpers.h

-- 
2.47.0

[bpf-next 1/4] selftests/bpf: watchdog timer for test_progs

[Eduard Zingerman]

This commit provides a watchdog timer that sets a limit of how long a
single sub-test could run:
- if sub-test runs for 10 seconds, the name of the test is printed
  (currently the name of the test is printed only after it finishes);
- if sub-test runs for 120 seconds, the running thread is terminated
  with SIGSEGV (to trigger crash_handler() and get a stack trace).

Specifically:
- the timer is armed on each call to run_one_test();
- re-armed at each call to test__start_subtest();
- is stopped when exiting run_one_test().

Default timeout could be overridden using '-w' or '--watchdog-timeout'
options. Value 0 can be used to turn the timer off.
Here is an example execution:

    $ ./ssh-exec.sh ./test_progs -w 5 -t \
      send_signal/send_signal_perf_thread_remote,send_signal/send_signal_nmi_thread_remote
    WATCHDOG: test case send_signal/send_signal_nmi_thread_remote executes for 5 seconds, terminating with SIGSEGV
    Caught signal #11!
    Stack trace:
    ./test_progs(crash_handler+0x1f)[0x9049ef]
    /lib64/libc.so.6(+0x40d00)[0x7f1f1184fd00]
    /lib64/libc.so.6(read+0x4a)[0x7f1f1191cc4a]
    ./test_progs[0x720dd3]
    ./test_progs[0x71ef7a]
    ./test_progs(test_send_signal+0x1db)[0x71edeb]
    ./test_progs[0x9066c5]
    ./test_progs(main+0x5ed)[0x9054ad]
    /lib64/libc.so.6(+0x2a088)[0x7f1f11839088]
    /lib64/libc.so.6(__libc_start_main+0x8b)[0x7f1f1183914b]
    ./test_progs(_start+0x25)[0x527385]
    #292     send_signal:FAIL
    test_send_signal_common:PASS:reading pipe 0 nsec
    test_send_signal_common:PASS:reading pipe error: size 0 0 nsec
    test_send_signal_common:PASS:incorrect result 0 nsec
    test_send_signal_common:PASS:pipe_write 0 nsec
    test_send_signal_common:PASS:setpriority 0 nsec

Timer is implemented using timer_{create,start} librt API.
Internally librt uses pthreads for SIGEV_THREAD timers,
so this change adds a background timer thread to the test process.
Because of this a few checks in tests 'bpf_iter' and 'iters'
need an update to account for an extra thread.

For parallelized scenario the watchdog is also created for each worker
fork. If one of the workers gets stuck, it would be terminated by a
watchdog. In theory, this might lead to a scenario when all worker
threads are exhausted, however this should not be a problem for
server_main(), as it would exit with some of the tests not run.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 .../selftests/bpf/prog_tests/bpf_iter.c       |   8 +-
 .../testing/selftests/bpf/prog_tests/iters.c  |   4 +-
 tools/testing/selftests/bpf/test_progs.c      | 104 ++++++++++++++++++
 tools/testing/selftests/bpf/test_progs.h      |   6 +
 4 files changed, 116 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index b8e1224cfd19..6f1bfacd7375 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/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);
 }
diff --git a/tools/testing/selftests/bpf/prog_tests/iters.c b/tools/testing/selftests/bpf/prog_tests/iters.c
index 89ff23c4a8bc..3cea71f9c500 100644
--- a/tools/testing/selftests/bpf/prog_tests/iters.c
+++ b/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++)
diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index 7421874380c2..6088d8222d59 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/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 @@ static int worker_main_send_subtests(int sock, struct test_state *state)
 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);
diff --git a/tools/testing/selftests/bpf/test_progs.h b/tools/testing/selftests/bpf/test_progs.h
index 7a58895867c3..74de33ae37e5 100644
--- a/tools/testing/selftests/bpf/test_progs.h
+++ b/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
-- 
2.47.0

[bpf-next 2/4] selftests/bpf: add read_with_timeout() utility function

[Eduard Zingerman]

int read_with_timeout(int fd, char *buf, size_t count, long usec)

As a regular read(2), but allows to specify a timeout in
micro-seconds. Returns -EAGAIN on timeout.
Implemented using select().

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 tools/testing/selftests/bpf/Makefile     |  1 +
 tools/testing/selftests/bpf/io_helpers.c | 21 +++++++++++++++++++++
 tools/testing/selftests/bpf/io_helpers.h |  7 +++++++
 3 files changed, 29 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/io_helpers.c
 create mode 100644 tools/testing/selftests/bpf/io_helpers.h

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index edef5df08cb2..b1080284522d 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/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		\
diff --git a/tools/testing/selftests/bpf/io_helpers.c b/tools/testing/selftests/bpf/io_helpers.c
new file mode 100644
index 000000000000..4ada0a74aa1f
--- /dev/null
+++ b/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;
+}
diff --git a/tools/testing/selftests/bpf/io_helpers.h b/tools/testing/selftests/bpf/io_helpers.h
new file mode 100644
index 000000000000..21e1134cd3ce
--- /dev/null
+++ b/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);
-- 
2.47.0

[bpf-next 3/4] selftests/bpf: allow send_signal test to timeout

[Eduard Zingerman]

The following invocation:

  $ t1=send_signal/send_signal_perf_thread_remote \
    t2=send_signal/send_signal_nmi_thread_remote  \
    ./test_progs -t $t1,$t2

Leads to send_signal_nmi_thread_remote to be stuck
on a line 180:

  /* wait for result */
  err = read(pipe_c2p[0], buf, 1);

In this test case:
- perf event PERF_COUNT_HW_CPU_CYCLES is created for parent process;
- BPF program is attached to perf event, and sends a signal to child
  process when event occurs;
- parent program burns some CPU in busy loop and calls read() to get
  notification from child that it received a signal.

The perf event is declared with .sample_period = 1.
This forces perf to throttle events, and under some unclear conditions
the event does not always occur while parent is in busy loop.
After parent enters read() system call CPU cycles event won't be
generated for parent anymore. Thus, if perf event had not occurred
already the test is stuck.

This commit updates the parent to wait for notification with a timeout,
doing several iterations of busy loop + read_with_timeout().

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 .../selftests/bpf/prog_tests/send_signal.c    | 32 +++++++++++--------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c
index 1aed94ec14ef..4e03d7a4c6f7 100644
--- a/tools/testing/selftests/bpf/prog_tests/send_signal.c
+++ b/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")) {
-- 
2.47.0

[bpf-next 4/4] selftests/bpf: update send_signal to lower perf evemts frequency

[Eduard Zingerman]

Similar to commit [1] sample perf events less often in
test_send_signal_nmi(). This should reduce perf events throttling.

[1] 7015843afcaf ("selftests/bpf: Fix send_signal test with nested CONFIG_PARAVIRT")

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 tools/testing/selftests/bpf/prog_tests/send_signal.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c
index 4e03d7a4c6f7..1702aa592c2c 100644
--- a/tools/testing/selftests/bpf/prog_tests/send_signal.c
+++ b/tools/testing/selftests/bpf/prog_tests/send_signal.c
@@ -229,7 +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,
 	};
-- 
2.47.0

Re: [bpf-next 0/4] selftests/bpf: fix for bpf_signal stalls, watchdog for test_progs

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Tue, 12 Nov 2024 03:09:02 -0800 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/4] selftests/bpf: watchdog timer for test_progs
    https://git.kernel.org/bpf/bpf-next/c/d9d4d127e813
  - [bpf-next,2/4] selftests/bpf: add read_with_timeout() utility function
    https://git.kernel.org/bpf/bpf-next/c/03066ed3105a
  - [bpf-next,3/4] selftests/bpf: allow send_signal test to timeout
    https://git.kernel.org/bpf/bpf-next/c/3209139d00e5
  - [bpf-next,4/4] selftests/bpf: update send_signal to lower perf evemts frequency
    https://git.kernel.org/bpf/bpf-next/c/4edab4c55d2d

You are awesome, thank you!
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