From: Jiri Olsa jolsa@kernel.org

[ Upstream commit 7fb27a56b9ebd8a77d9dd188e8a42bff99bc3443 ]

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 hide some functions from ftrace, but meanwhile we workaround this by skipping bpf_dispatcher_xdp_func from kprobe_multi bench test.

Reported-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Jiri Olsa jolsa@kernel.org Signed-off-by: Andrii Nakryiko andrii@kernel.org Acked-by: Yonghong Song yhs@fb.com Link: https://lore.kernel.org/bpf/20220714082316.479181-1-jolsa@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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..48681bf73e0b 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 (!strcmp(name, "bpf_dispatcher_xdp_func")) + continue; if (!strncmp(name, "__ftrace_invalid_address__", sizeof("__ftrace_invalid_address__") - 1)) continue;