Re: [bpf-next v4 2/2] selftests/bpf: add test case for htab map

[Tonghao Zhang <tong@infragraf.org>]

> On Jan 10, 2023, at 9:33 AM, Martin KaFai Lau <martin.lau@linux.dev> wrote:
> 
> On 1/5/23 1:26 AM, tong@infragraf.org wrote:
>> diff --git a/tools/testing/selftests/bpf/prog_tests/htab_deadlock.c b/tools/testing/selftests/bpf/prog_tests/htab_deadlock.c
>> new file mode 100644
>> index 000000000000..137dce8f1346
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/prog_tests/htab_deadlock.c
>> @@ -0,0 +1,75 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2022 DiDi Global Inc. */
>> +#define _GNU_SOURCE
>> +#include <pthread.h>
>> +#include <sched.h>
>> +#include <test_progs.h>
>> +
>> +#include "htab_deadlock.skel.h"
>> +
>> +static int perf_event_open(void)
>> +{
>> +	struct perf_event_attr attr = {0};
>> +	int pfd;
>> +
>> +	/* create perf event on CPU 0 */
>> +	attr.size = sizeof(attr);
>> +	attr.type = PERF_TYPE_HARDWARE;
>> +	attr.config = PERF_COUNT_HW_CPU_CYCLES;
>> +	attr.freq = 1;
>> +	attr.sample_freq = 1000;
>> +	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
>> +
>> +	return pfd >= 0 ? pfd : -errno;
>> +}
>> +
>> +void test_htab_deadlock(void)
>> +{
>> +	unsigned int val = 0, key = 20;
>> +	struct bpf_link *link = NULL;
>> +	struct htab_deadlock *skel;
>> +	int err, i, pfd;
>> +	cpu_set_t cpus;
>> +
>> +	skel = htab_deadlock__open_and_load();
>> +	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
>> +		return;
>> +
>> +	err = htab_deadlock__attach(skel);
>> +	if (!ASSERT_OK(err, "skel_attach"))
>> +		goto clean_skel;
>> +
>> +	/* NMI events. */
>> +	pfd = perf_event_open();
>> +	if (pfd < 0) {
>> +		if (pfd == -ENOENT || pfd == -EOPNOTSUPP) {
>> +			printf("%s:SKIP:no PERF_COUNT_HW_CPU_CYCLES\n", __func__);
>> +			test__skip();
> 
> This test is a SKIP in bpf CI, so it won't be useful.
> https://github.com/kernel-patches/bpf/actions/runs/3858084722/jobs/6579470256#step:6:5198
> 
> Is there other way to test it or do you know what may be missing in vmtest.sh? Not sure if the cloud setup in CI blocks HW_CPU_CYCLES.  If it is, I also don't know a good way (Cc: Manu).
Hi

Other test cases using PERF_COUNT_HW_CPU_CYCLES were skipped too. For example,
send_signal
find_vma
get_stackid_cannot_attach

> 
>> +			goto clean_skel;
>> +		}
>> +		if (!ASSERT_GE(pfd, 0, "perf_event_open"))
>> +			goto clean_skel;
>> +	}
>> +
>> +	link = bpf_program__attach_perf_event(skel->progs.bpf_empty, pfd);
>> +	if (!ASSERT_OK_PTR(link, "attach_perf_event"))
>> +		goto clean_pfd;
>> +
>> +	/* Pinned on CPU 0 */
>> +	CPU_ZERO(&cpus);
>> +	CPU_SET(0, &cpus);
>> +	pthread_setaffinity_np(pthread_self(), sizeof(cpus), &cpus);
>> +
>> +	/* update bpf map concurrently on CPU0 in NMI and Task context.
>> +	 * there should be no kernel deadlock.
>> +	 */
>> +	for (i = 0; i < 100000; i++)
>> +		bpf_map_update_elem(bpf_map__fd(skel->maps.htab),
>> +				    &key, &val, BPF_ANY);
>> +
>> +	bpf_link__destroy(link);
>> +clean_pfd:
>> +	close(pfd);
>> +clean_skel:
>> +	htab_deadlock__destroy(skel);
>> +}
>> diff --git a/tools/testing/selftests/bpf/progs/htab_deadlock.c b/tools/testing/selftests/bpf/progs/htab_deadlock.c
>> new file mode 100644
>> index 000000000000..dacd003b1ccb
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/htab_deadlock.c
>> @@ -0,0 +1,30 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2022 DiDi Global Inc. */
>> +#include <linux/bpf.h>
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +struct {
>> +	__uint(type, BPF_MAP_TYPE_HASH);
>> +	__uint(max_entries, 2);
>> +	__uint(map_flags, BPF_F_ZERO_SEED);
>> +	__type(key, unsigned int);
>> +	__type(value, unsigned int);
>> +} htab SEC(".maps");
>> +
>> +SEC("fentry/perf_event_overflow")
>> +int bpf_nmi_handle(struct pt_regs *regs)
>> +{
>> +	unsigned int val = 0, key = 4;
>> +
>> +	bpf_map_update_elem(&htab, &key, &val, BPF_ANY);
> 
> I ran it in my qemu setup which does not skip the test.  I got this splat though:
This is a false alarm, not deadlock(this patch fix deadlock, only). I fix waring in other patch, please review
https://patchwork.kernel.org/project/netdevbpf/patch/20230105112749.38421-1-tong@infragraf.org/ 
> 
> [   42.990306] ================================
> [   42.990307] WARNING: inconsistent lock state
> [   42.990310] 6.2.0-rc2-00304-gaf88a1bb9967 #409 Tainted: G           O
> [   42.990313] --------------------------------
> [   42.990315] inconsistent {INITIAL USE} -> {IN-NMI} usage.
> [   42.990317] test_progs/1546 [HC1[1]:SC0[0]:HE0:SE1] takes:
> [   42.990322] ffff888101245768 (&htab->lockdep_key){....}-{2:2}, at: htab_map_update_elem+0x1e7/0x810
> [   42.990340] {INITIAL USE} state was registered at:
> [   42.990341]   lock_acquire+0x1e6/0x530
> [   42.990351]   _raw_spin_lock_irqsave+0xb8/0x100
> [   42.990362]   htab_map_update_elem+0x1e7/0x810
> [   42.990365]   bpf_map_update_value+0x40d/0x4f0
> [   42.990371]   map_update_elem+0x423/0x580
> [   42.990375]   __sys_bpf+0x54e/0x670
> [   42.990377]   __x64_sys_bpf+0x7c/0x90
> [   42.990382]   do_syscall_64+0x43/0x90
> [   42.990387]   entry_SYSCALL_64_after_hwframe+0x72/0xdc
> 
> Please check.
> 
>> +	return 0;
>> +}
>> +
>> +SEC("perf_event")
>> +int bpf_empty(struct pt_regs *regs)
>> +{
> 
> btw, from a quick look at __perf_event_overflow, I suspect doing the bpf_map_update_elem() here instead of the fentry/perf_event_overflow above can also reproduce the patch 1 issue?
No
bpf_overflow_handler will check the bpf_prog_active, if syscall increase it, bpf_overflow_handler will skip the bpf prog.
Fentry will not check the bpf_prog_active, and interrupt the task context. We have discussed that. 

> 
>> +	return 0;
>> +}
> 
>