From 67ee5ad27d5101be4e9e8980c0734a0423bfd0a7 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Tue, 3 Feb 2026 21:51:45 -0800 Subject: [PATCH] selftests/bpf: Add a testcase for deadlock avoidance Add a testcase that checks that deadlock avoidance is working as expected. Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260204055147.54960-3-alexei.starovoitov@gmail.com --- .../bpf/prog_tests/timer_start_deadlock.c | 33 ++++++++ .../bpf/progs/timer_start_deadlock.c | 75 +++++++++++++++++++ 2 files changed, 108 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/timer_start_deadlock.c create mode 100644 tools/testing/selftests/bpf/progs/timer_start_deadlock.c diff --git a/tools/testing/selftests/bpf/prog_tests/timer_start_deadlock.c b/tools/testing/selftests/bpf/prog_tests/timer_start_deadlock.c new file mode 100644 index 0000000000000..9f1f9aec88880 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/timer_start_deadlock.c @@ -0,0 +1,33 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ +#include +#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); +} diff --git a/tools/testing/selftests/bpf/progs/timer_start_deadlock.c b/tools/testing/selftests/bpf/progs/timer_start_deadlock.c new file mode 100644 index 0000000000000..368563747a469 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/timer_start_deadlock.c @@ -0,0 +1,75 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ +#include +#include +#include + +#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; +} -- 2.47.3