Re: [bpf-next v3 2/2] selftests/bpf: add test case for htab map

[Yonghong Song <yhs@meta.com>]

On 12/18/22 8:15 PM, xiangxia.m.yue@gmail.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> 
> This testing show how to reproduce deadlock in special case.
> We update htab map in Task and NMI context. Task can be interrupted by
> NMI, if the same map bucket was locked, there will be a deadlock.
> 
> * map max_entries is 2.
> * NMI using key 4 and Task context using key 20.
> * so same bucket index but map_locked index is different.
> 
> The selftest use perf to produce the NMI and fentry nmi_handle.
> Note that bpf_overflow_handler checks bpf_prog_active, but in bpf update
> map syscall increase this counter in bpf_disable_instrumentation.
> Then fentry nmi_handle and update hash map will reproduce the issue.
> 
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Andrii Nakryiko <andrii@kernel.org>
> Cc: Martin KaFai Lau <martin.lau@linux.dev>
> Cc: Song Liu <song@kernel.org>
> Cc: Yonghong Song <yhs@fb.com>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: KP Singh <kpsingh@kernel.org>
> Cc: Stanislav Fomichev <sdf@google.com>
> Cc: Hao Luo <haoluo@google.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Hou Tao <houtao1@huawei.com>
> Acked-by: Yonghong Song <yhs@fb.com>
> ---
>   tools/testing/selftests/bpf/DENYLIST.aarch64  |  1 +
>   tools/testing/selftests/bpf/DENYLIST.s390x    |  1 +
>   .../selftests/bpf/prog_tests/htab_deadlock.c  | 75 +++++++++++++++++++
>   .../selftests/bpf/progs/htab_deadlock.c       | 32 ++++++++
>   4 files changed, 109 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/htab_deadlock.c
>   create mode 100644 tools/testing/selftests/bpf/progs/htab_deadlock.c
> 
> diff --git a/tools/testing/selftests/bpf/DENYLIST.aarch64 b/tools/testing/selftests/bpf/DENYLIST.aarch64
> index 99cc33c51eaa..87e8fc9c9df2 100644
> --- a/tools/testing/selftests/bpf/DENYLIST.aarch64
> +++ b/tools/testing/selftests/bpf/DENYLIST.aarch64
> @@ -24,6 +24,7 @@ fexit_test                                       # fexit_attach unexpected error
>   get_func_args_test                               # get_func_args_test__attach unexpected error: -524 (errno 524) (trampoline)
>   get_func_ip_test                                 # get_func_ip_test__attach unexpected error: -524 (errno 524) (trampoline)
>   htab_update/reenter_update
> +htab_deadlock                                    # failed to find kernel BTF type ID of 'nmi_handle': -3 (trampoline)
>   kfree_skb                                        # attach fentry unexpected error: -524 (trampoline)
>   kfunc_call/subprog                               # extern (var ksym) 'bpf_prog_active': not found in kernel BTF
>   kfunc_call/subprog_lskel                         # skel unexpected error: -2
> diff --git a/tools/testing/selftests/bpf/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
> index 585fcf73c731..735239b31050 100644
> --- a/tools/testing/selftests/bpf/DENYLIST.s390x
> +++ b/tools/testing/selftests/bpf/DENYLIST.s390x
> @@ -26,6 +26,7 @@ get_func_args_test	                 # trampoline
>   get_func_ip_test                         # get_func_ip_test__attach unexpected error: -524                             (trampoline)
>   get_stack_raw_tp                         # user_stack corrupted user stack                                             (no backchain userspace)
>   htab_update                              # failed to attach: ERROR: strerror_r(-524)=22                                (trampoline)
> +htab_deadlock                            # failed to find kernel BTF type ID of 'nmi_handle': -3                       (trampoline)
>   kfree_skb                                # attach fentry unexpected error: -524                                        (trampoline)
>   kfunc_call                               # 'bpf_prog_active': not found in kernel BTF                                  (?)
>   kfunc_dynptr_param                       # JIT does not support calling kernel function                                (kfunc)
> 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();
> +			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..d394f95e97c3
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/htab_deadlock.c
> @@ -0,0 +1,32 @@
> +// 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");
> +
> +/* nmi_handle on x86 platform. If changing keyword
> + * "static" to "inline", this prog load failed. */
> +SEC("fentry/nmi_handle")

The above comment is not what I mean. In arch/x86/kernel/nmi.c,
we have
   static int nmi_handle(unsigned int type, struct pt_regs *regs)
   {
        ...
   }
   ...
   static noinstr void default_do_nmi(struct pt_regs *regs)
   {
        ...
        handled = nmi_handle(NMI_LOCAL, regs);
        ...
   }

Since nmi_handle is a static function, it is possible that
the function might be inlined in default_do_nmi by the
compiler. If this happens, fentry/nmi_handle will not
be triggered and the test will pass.

So I suggest to change the comment to
   nmi_handle() is a static function and might be
   inlined into its caller. If this happens, the
   test can still pass without previous kernel fix.

> +int bpf_nmi_handle(struct pt_regs *regs)
> +{
> +	unsigned int val = 0, key = 4;
> +
> +	bpf_map_update_elem(&htab, &key, &val, BPF_ANY);
> +	return 0;
> +}
> +
> +SEC("perf_event")
> +int bpf_empty(struct pt_regs *regs)
> +{
> +	return 0;
> +}