Commit 50bd5a0c authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Daniel Borkmann
Browse files

selftests/bpf: Add timer lockup selftest 



Add a selftest that tries to trigger a situation where two timer callbacks
are attempting to cancel each other's timer. By running them continuously,
we hit a condition where both run in parallel and cancel each other.

Without the fix in the previous patch, this would cause a lockup as
hrtimer_cancel on either side will wait for forward progress from the
callback.

Ensure that this situation leads to a EDEADLK error.

Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240711052709.2148616-1-memxor@gmail.com
parent 0c237341

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

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// SPDX-License-Identifier: GPL-2.0



#define _GNU_SOURCE

#include <sched.h>

#include <test_progs.h>

#include <pthread.h>

#include <network_helpers.h>



#include "timer_lockup.skel.h"



static long cpu;

static int *timer1_err;

static int *timer2_err;

static bool skip;



volatile int k = 0;



static void *timer_lockup_thread(void *arg)

{

	LIBBPF_OPTS(bpf_test_run_opts, opts,

		.data_in	= &pkt_v4,

		.data_size_in	= sizeof(pkt_v4),

		.repeat		= 1000,

	);

	int i, prog_fd = *(int *)arg;

	cpu_set_t cpuset;



	CPU_ZERO(&cpuset);

	CPU_SET(__sync_fetch_and_add(&cpu, 1), &cpuset);

	ASSERT_OK(pthread_setaffinity_np(pthread_self(), sizeof(cpuset),

				         &cpuset),

		  "cpu affinity");



	for (i = 0; !READ_ONCE(*timer1_err) && !READ_ONCE(*timer2_err); i++) {

		bpf_prog_test_run_opts(prog_fd, &opts);

		/* Skip the test if we can't reproduce the race in a reasonable

		 * amount of time.

		 */

		if (i > 50) {

			WRITE_ONCE(skip, true);

			break;

		}

	}



	return NULL;

}



void test_timer_lockup(void)

{

	int timer1_prog, timer2_prog;

	struct timer_lockup *skel;

	pthread_t thrds[2];

	void *ret;



	skel = timer_lockup__open_and_load();

	if (!ASSERT_OK_PTR(skel, "timer_lockup__open_and_load"))

		return;



	timer1_prog = bpf_program__fd(skel->progs.timer1_prog);

	timer2_prog = bpf_program__fd(skel->progs.timer2_prog);



	timer1_err = &skel->bss->timer1_err;

	timer2_err = &skel->bss->timer2_err;



	if (!ASSERT_OK(pthread_create(&thrds[0], NULL, timer_lockup_thread,

				      &timer1_prog),

		       "pthread_create thread1"))

		goto out;

	if (!ASSERT_OK(pthread_create(&thrds[1], NULL, timer_lockup_thread,

				      &timer2_prog),

		       "pthread_create thread2")) {

		pthread_exit(&thrds[0]);

		goto out;

	}



	pthread_join(thrds[1], &ret);

	pthread_join(thrds[0], &ret);



	if (skip) {

		test__skip();

		goto out;

	}



	if (*timer1_err != -EDEADLK && *timer1_err != 0)

		ASSERT_FAIL("timer1_err bad value");

	if (*timer2_err != -EDEADLK && *timer2_err != 0)

		ASSERT_FAIL("timer2_err bad value");

out:

	timer_lockup__destroy(skel);

	return;

}

tools/testing/selftests/bpf/progs/timer_lockup.c

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// SPDX-License-Identifier: GPL-2.0



#include <linux/bpf.h>

#include <time.h>

#include <errno.h>

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>

#include "bpf_misc.h"



char _license[] SEC("license") = "GPL";



struct elem {

	struct bpf_timer t;

};



struct {

	__uint(type, BPF_MAP_TYPE_ARRAY);

	__uint(max_entries, 1);

	__type(key, int);

	__type(value, struct elem);

} timer1_map SEC(".maps");



struct {

	__uint(type, BPF_MAP_TYPE_ARRAY);

	__uint(max_entries, 1);

	__type(key, int);

	__type(value, struct elem);

} timer2_map SEC(".maps");



int timer1_err;

int timer2_err;



static int timer_cb1(void *map, int *k, struct elem *v)

{

	struct bpf_timer *timer;

	int key = 0;



	timer = bpf_map_lookup_elem(&timer2_map, &key);

	if (timer)

		timer2_err = bpf_timer_cancel(timer);



	return 0;

}



static int timer_cb2(void *map, int *k, struct elem *v)

{

	struct bpf_timer *timer;

	int key = 0;



	timer = bpf_map_lookup_elem(&timer1_map, &key);

	if (timer)

		timer1_err = bpf_timer_cancel(timer);



	return 0;

}



SEC("tc")

int timer1_prog(void *ctx)

{

	struct bpf_timer *timer;

	int key = 0;



	timer = bpf_map_lookup_elem(&timer1_map, &key);

	if (timer) {

		bpf_timer_init(timer, &timer1_map, CLOCK_BOOTTIME);

		bpf_timer_set_callback(timer, timer_cb1);

		bpf_timer_start(timer, 1, BPF_F_TIMER_CPU_PIN);

	}



	return 0;

}



SEC("tc")

int timer2_prog(void *ctx)

{

	struct bpf_timer *timer;

	int key = 0;



	timer = bpf_map_lookup_elem(&timer2_map, &key);

	if (timer) {

		bpf_timer_init(timer, &timer2_map, CLOCK_BOOTTIME);

		bpf_timer_set_callback(timer, timer_cb2);

		bpf_timer_start(timer, 1, BPF_F_TIMER_CPU_PIN);

	}



	return 0;

}