On Thu, Jul 14, 2022 at 01:01:30PM -0700, Yonghong Song wrote: > > > On 7/14/22 1:23 AM, Jiri Olsa wrote: > > Alexei reported crash by running test_progs -j on system > > with 32 cpus. > > > > It turned out the kprobe_multi bench test that attaches all > > ftrace-able functions will race with bpf_dispatcher_update, > > that calls bpf_arch_text_poke on bpf_dispatcher_xdp_func, > > which is ftrace-able function. > > > > Ftrace is not aware of this update so this will cause > > ftrace_bug with: > > > > WARNING: CPU: 6 PID: 1985 at > > arch/x86/kernel/ftrace.c:94 ftrace_verify_code+0x27/0x50 > > ... > > ftrace_replace_code+0xa3/0x170 > > ftrace_modify_all_code+0xbd/0x150 > > ftrace_startup_enable+0x3f/0x50 > > ftrace_startup+0x98/0xf0 > > register_ftrace_function+0x20/0x60 > > register_fprobe_ips+0xbb/0xd0 > > bpf_kprobe_multi_link_attach+0x179/0x430 > > __sys_bpf+0x18a1/0x2440 > > ... > > ------------[ ftrace bug ]------------ > > ftrace failed to modify > > [<ffffffff818d9380>] bpf_dispatcher_xdp_func+0x0/0x10 > > actual: ffffffe9:7b:ffffff9c:77:1e > > Setting ftrace call site to call ftrace function > > > > It looks like we need some way to way to hide some functions > > need some way to hide some functions ... ugh, right > > > from ftrace, but meanwhile we workaround this by skipping > > bpf_dispatcher_xdp_func from kprobe_multi bench test. > > > > Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx> > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > > I tried with 32cpus on my local qemu/vm but cannot reproduce the crash. > But look at the code, your should seem okay as bpf_dispatcher_xdp_func > indeed could be poked and simplified. So with a few nits, > > Acked-by: Yonghong Song <yhs@xxxxxx> > > > --- > > tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c > > index 5b93d5d0bd93..8c442051f312 100644 > > --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c > > +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c > > @@ -364,6 +364,8 @@ static int get_syms(char ***symsp, size_t *cntp) > > continue; > > if (!strncmp(name, "rcu_", 4)) > > continue; > > + if (!strncmp(name, "bpf_dispatcher_xdp_func", 23)) > > ffffffff81b17a90 T bpf_dispatcher_xdp_func > > bpf_dispatcher_xdp_func is a full name, you can just use strcmp here. > Further, > > linux/bpf.h:#define BPF_DISPATCHER_FUNC(name) bpf_dispatcher_##name##_func > > Currently, bpf_dispatcher_xdp_func is the ONLY BPF_DISPATCHER_FUNC. > So comparing bpf_dispatcher_xdp_func is enough. It would be good > to add a comment to explain why not comparing to bpf_dispatcher_*_func. ok thanks, jirka
