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 ...
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.
+ continue;
if (!strncmp(name, "__ftrace_invalid_address__",
sizeof("__ftrace_invalid_address__") - 1))
continue;
