Commit 0a5d2efa authored by Hou Tao's avatar Hou Tao Committed by Alexei Starovoitov
Browse files

selftests/bpf: Add test case for the freeing of bpf_timer 



The main purpose of the test is to demonstrate the lock problem for the
free of bpf_timer under PREEMPT_RT. When freeing a bpf_timer which is
running on other CPU in bpf_timer_cancel_and_free(), hrtimer_cancel()
will try to acquire a spin-lock (namely softirq_expiry_lock), however
the freeing procedure has already held a raw-spin-lock.

The test first creates two threads: one to start timers and the other to
free timers. The start-timers thread will start the timer and then wake
up the free-timers thread to free these timers when the starts complete.
After freeing, the free-timer thread will wake up the start-timer thread
to complete the current iteration. A loop of 10 iterations is used.

Signed-off-by: default avatarHou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20250117101816.2101857-6-houtao@huaweicloud.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 58f038e6

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

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// SPDX-License-Identifier: GPL-2.0

/* Copyright (C) 2025. Huawei Technologies Co., Ltd */

#define _GNU_SOURCE

#include <unistd.h>

#include <sys/syscall.h>

#include <test_progs.h>



#include "free_timer.skel.h"



struct run_ctx {

	struct bpf_program *start_prog;

	struct bpf_program *overwrite_prog;

	pthread_barrier_t notify;

	int loop;

	bool start;

	bool stop;

};



static void start_threads(struct run_ctx *ctx)

{

	ctx->start = true;

}



static void stop_threads(struct run_ctx *ctx)

{

	ctx->stop = true;

	/* Guarantee the order between ->stop and ->start */

	__atomic_store_n(&ctx->start, true, __ATOMIC_RELEASE);

}



static int wait_for_start(struct run_ctx *ctx)

{

	while (!__atomic_load_n(&ctx->start, __ATOMIC_ACQUIRE))

		usleep(10);



	return ctx->stop;

}



static void *overwrite_timer_fn(void *arg)

{

	struct run_ctx *ctx = arg;

	int loop, fd, err;

	cpu_set_t cpuset;

	long ret = 0;



	/* Pin on CPU 0 */

	CPU_ZERO(&cpuset);

	CPU_SET(0, &cpuset);

	pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);



	/* Is the thread being stopped ? */

	err = wait_for_start(ctx);

	if (err)

		return NULL;



	fd = bpf_program__fd(ctx->overwrite_prog);

	loop = ctx->loop;

	while (loop-- > 0) {

		LIBBPF_OPTS(bpf_test_run_opts, opts);



		/* Wait for start thread to complete */

		pthread_barrier_wait(&ctx->notify);



		/* Overwrite timers */

		err = bpf_prog_test_run_opts(fd, &opts);

		if (err)

			ret |= 1;

		else if (opts.retval)

			ret |= 2;



		/* Notify start thread to start timers */

		pthread_barrier_wait(&ctx->notify);

	}



	return (void *)ret;

}



static void *start_timer_fn(void *arg)

{

	struct run_ctx *ctx = arg;

	int loop, fd, err;

	cpu_set_t cpuset;

	long ret = 0;



	/* Pin on CPU 1 */

	CPU_ZERO(&cpuset);

	CPU_SET(1, &cpuset);

	pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);



	/* Is the thread being stopped ? */

	err = wait_for_start(ctx);

	if (err)

		return NULL;



	fd = bpf_program__fd(ctx->start_prog);

	loop = ctx->loop;

	while (loop-- > 0) {

		LIBBPF_OPTS(bpf_test_run_opts, opts);



		/* Run the prog to start timer */

		err = bpf_prog_test_run_opts(fd, &opts);

		if (err)

			ret |= 4;

		else if (opts.retval)

			ret |= 8;



		/* Notify overwrite thread to do overwrite */

		pthread_barrier_wait(&ctx->notify);



		/* Wait for overwrite thread to complete */

		pthread_barrier_wait(&ctx->notify);

	}



	return (void *)ret;

}



void test_free_timer(void)

{

	struct free_timer *skel;

	struct bpf_program *prog;

	struct run_ctx ctx;

	pthread_t tid[2];

	void *ret;

	int err;



	skel = free_timer__open_and_load();

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

		return;



	memset(&ctx, 0, sizeof(ctx));



	prog = bpf_object__find_program_by_name(skel->obj, "start_timer");

	if (!ASSERT_OK_PTR(prog, "find start prog"))

		goto out;

	ctx.start_prog = prog;



	prog = bpf_object__find_program_by_name(skel->obj, "overwrite_timer");

	if (!ASSERT_OK_PTR(prog, "find overwrite prog"))

		goto out;

	ctx.overwrite_prog = prog;



	pthread_barrier_init(&ctx.notify, NULL, 2);

	ctx.loop = 10;



	err = pthread_create(&tid[0], NULL, start_timer_fn, &ctx);

	if (!ASSERT_OK(err, "create start_timer"))

		goto out;



	err = pthread_create(&tid[1], NULL, overwrite_timer_fn, &ctx);

	if (!ASSERT_OK(err, "create overwrite_timer")) {

		stop_threads(&ctx);

		goto out;

	}



	start_threads(&ctx);



	ret = NULL;

	err = pthread_join(tid[0], &ret);

	ASSERT_EQ(err | (long)ret, 0, "start_timer");

	ret = NULL;

	err = pthread_join(tid[1], &ret);

	ASSERT_EQ(err | (long)ret, 0, "overwrite_timer");

out:

	free_timer__destroy(skel);

}

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

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// SPDX-License-Identifier: GPL-2.0

/* Copyright (C) 2025. Huawei Technologies Co., Ltd */

#include <linux/bpf.h>

#include <time.h>

#include <bpf/bpf_tracing.h>

#include <bpf/bpf_helpers.h>



#define MAX_ENTRIES 8



struct map_value {

	struct bpf_timer timer;

};



struct {

	__uint(type, BPF_MAP_TYPE_HASH);

	__type(key, int);

	__type(value, struct map_value);

	__uint(max_entries, MAX_ENTRIES);

} map SEC(".maps");



static int timer_cb(void *map, void *key, struct map_value *value)

{

	volatile int sum = 0;

	int i;



	bpf_for(i, 0, 1024 * 1024) sum += i;



	return 0;

}



static int start_cb(int key)

{

	struct map_value *value;



	value = bpf_map_lookup_elem(&map, (void *)&key);

	if (!value)

		return 0;



	bpf_timer_init(&value->timer, &map, CLOCK_MONOTONIC);

	bpf_timer_set_callback(&value->timer, timer_cb);

	/* Hope 100us will be enough to wake-up and run the overwrite thread */

	bpf_timer_start(&value->timer, 100000, BPF_F_TIMER_CPU_PIN);



	return 0;

}



static int overwrite_cb(int key)

{

	struct map_value zero = {};



	/* Free the timer which may run on other CPU */

	bpf_map_update_elem(&map, (void *)&key, &zero, BPF_ANY);



	return 0;

}



SEC("syscall")

int BPF_PROG(start_timer)

{

	bpf_loop(MAX_ENTRIES, start_cb, NULL, 0);

	return 0;

}



SEC("syscall")

int BPF_PROG(overwrite_timer)

{

	bpf_loop(MAX_ENTRIES, overwrite_cb, NULL, 0);

	return 0;

}



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