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: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240711052709.2148616-1-memxor@gmail.com

diff --git a/tools/testing/selftests/bpf/prog_tests/timer_lockup.c b/tools/testing/selftests/bpf/prog_tests/timer_lockup.c
new file mode 100644 (file)
index 0000000..871d16c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/timer_lockup.c
@@ -0,0 +1,91 @@
+// 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;
+}

diff --git a/tools/testing/selftests/bpf/progs/timer_lockup.c b/tools/testing/selftests/bpf/progs/timer_lockup.c
new file mode 100644 (file)
index 0000000..3e52013
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/timer_lockup.c
@@ -0,0 +1,87 @@
+// 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;
+}