On Tue, Dec 27, 2022 at 8:43 PM Yonghong Song <yhs@xxxxxxxx> wrote:
>
>
>
> On 12/18/22 8:15 PM, xiangxia.m.yue@xxxxxxxxx wrote:
> > From: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
> > Cc: Song Liu <song@xxxxxxxxxx>
> > Cc: Yonghong Song <yhs@xxxxxx>
> > Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> > Cc: KP Singh <kpsingh@xxxxxxxxxx>
> > Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > Cc: Hao Luo <haoluo@xxxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: Hou Tao <houtao1@xxxxxxxxxx>
> > Acked-by: Yonghong Song <yhs@xxxxxx>
> > ---
> > 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.
It's worse than this.
fentry is buggy.
We shouldn't allow attaching fentry to:
NOKPROBE_SYMBOL(nmi_handle);
