Commit 67ee5ad2 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Andrii Nakryiko
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selftests/bpf: Add a testcase for deadlock avoidance 



Add a testcase that checks that deadlock avoidance is working
as expected.

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260204055147.54960-3-alexei.starovoitov@gmail.com
parent 7d49635e

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

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// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */

#include <test_progs.h>

#include "timer_start_deadlock.skel.h"



void test_timer_start_deadlock(void)

{

	struct timer_start_deadlock *skel;

	int err, prog_fd;

	LIBBPF_OPTS(bpf_test_run_opts, opts);



	skel = timer_start_deadlock__open_and_load();

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

		return;



	err = timer_start_deadlock__attach(skel);

	if (!ASSERT_OK(err, "skel_attach"))

		goto cleanup;



	prog_fd = bpf_program__fd(skel->progs.start_timer);



	/*

	 * Run the syscall program that attempts to deadlock.

	 * If the kernel deadlocks, this call will never return.

	 */

	err = bpf_prog_test_run_opts(prog_fd, &opts);

	ASSERT_OK(err, "prog_test_run");

	ASSERT_EQ(opts.retval, 0, "prog_retval");



	ASSERT_EQ(skel->bss->tp_called, 1, "tp_called");

cleanup:

	timer_start_deadlock__destroy(skel);

}

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

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// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */

#include <vmlinux.h>

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>



#define CLOCK_MONOTONIC 1



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



struct elem {

	struct bpf_timer timer;

};



struct {

	__uint(type, BPF_MAP_TYPE_ARRAY);

	__uint(max_entries, 1);

	__type(key, int);

	__type(value, struct elem);

} timer_map SEC(".maps");



volatile int in_timer_start;

volatile int tp_called;



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

{

	return 0;

}



SEC("tp_btf/hrtimer_cancel")

int BPF_PROG(tp_hrtimer_cancel, struct hrtimer *hrtimer)

{

	struct bpf_timer *timer;

	static bool called = false;

	int key = 0;



	if (!in_timer_start)

		return 0;



	tp_called = 1;

	timer = bpf_map_lookup_elem(&timer_map, &key);



	/*

	 * Call bpf_timer_start() from the tracepoint within hrtimer logic

	 * on the same timer to make sure it doesn't deadlock,

	 * and do it once.

	 */

	if (!called) {

		called = true;

		bpf_timer_start(timer, 1000000000, 0);

	}

	return 0;

}



SEC("syscall")

int start_timer(void *ctx)

{

	struct bpf_timer *timer;

	int key = 0;



	timer = bpf_map_lookup_elem(&timer_map, &key);

	/* claude may complain here that there is no NULL check. Ignoring it. */

	bpf_timer_init(timer, &timer_map, CLOCK_MONOTONIC);

	bpf_timer_set_callback(timer, timer_cb);



	/*

	 * call hrtimer_start() twice, so that 2nd call does

	 * remove_hrtimer() and trace_hrtimer_cancel() tracepoint.

	 */

	in_timer_start = 1;

	bpf_timer_start(timer, 1000000000, 0);

	bpf_timer_start(timer, 1000000000, 0);

	in_timer_start = 0;

	return 0;

}