On Sat, Mar 18, 2023 at 12:41 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Fri, Mar 17, 2023 at 4:49 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > It hits below warning on my test machine when running test_progs,
> >
> > [ 702.223611] ------------[ cut here ]------------
> > [ 702.224168] RCU not on for: preempt_count_sub+0x0/0xa0
> > [ 702.224770] WARNING: CPU: 14 PID: 5267 at include/linux/trace_recursion.h:162 fprobe_handler.part.0+0x1b8/0x1c0
> > [ 702.231740] CPU: 14 PID: 5267 Comm: main_amd64 Kdump: loaded Tainted: G O 6.2.0+ #584
> > [ 702.233169] RIP: 0010:fprobe_handler.part.0+0x1b8/0x1c0
> > [ 702.241388] Call Trace:
> > [ 702.241615] <TASK>
> > [ 702.241811] fprobe_handler+0x22/0x30
> > [ 702.242129] 0xffffffffc04710f7
> > [ 702.242417] RIP: 0010:preempt_count_sub+0x5/0xa0
> > [ 702.242809] Code: c8 50 68 94 42 0e b5 48 cf e9 f9 fd ff ff 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 e8 4b cd 38 0b <55> 8b 0d 9c d0 cf 02 48 89 e5 85 c9 75 1b 65 8b 05 be 78 f4 4a 89
> > [ 702.244752] RSP: 0018:ffffaf6187d27f10 EFLAGS: 00000082 ORIG_RAX: 0000000000000000
> > [ 702.245801] RAX: 000000000000000e RBX: 0000000001b6ab72 RCX: 0000000000000000
> > [ 702.246804] RDX: 0000000000000000 RSI: ffffffffb627967d RDI: 0000000000000001
> > [ 702.247801] RBP: ffffaf6187d27f30 R08: 0000000000000000 R09: 0000000000000000
> > [ 702.248786] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000000ca
> > [ 702.249782] R13: ffffaf6187d27f58 R14: 0000000000000000 R15: 0000000000000000
> > [ 702.250785] ? preempt_count_sub+0x5/0xa0
> > [ 702.251540] ? syscall_enter_from_user_mode+0x96/0xc0
> > [ 702.252368] ? preempt_count_sub+0x5/0xa0
> > [ 702.253104] ? syscall_enter_from_user_mode+0x96/0xc0
> > [ 702.253918] do_syscall_64+0x16/0x90
> > [ 702.254613] entry_SYSCALL_64_after_hwframe+0x72/0xdc
> > [ 702.255422] RIP: 0033:0x46b793
> >
> > It's caused by bench test attaching kprobe_multi link to preempt_count_sub
> > function, which is not executed in rcu safe context so the kprobe handler
> > on top of it will trigger the rcu warning.
> >
> > Filtering out preempt_count_ functions from the bench test.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > ---
> > 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 22be0a9..5561b93 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> > @@ -379,6 +379,8 @@ static int get_syms(char ***symsp, size_t *cntp, bool kernel)
> > if (!strncmp(name, "__ftrace_invalid_address__",
> > sizeof("__ftrace_invalid_address__") - 1))
> > continue;
> > + if (!strncmp(name, "preempt_count_", strlen("preempt_count_")))
> > + continue;
> >
>
> let's add str_has_pfx() helper macro from libbpf_internal.h to
> test_progs.h and use that instead of repeating each substring twice?
>
Thanks for the suggestion.
> Here's what libbpf is doing:
>
> /* Check whether a string `str` has prefix `pfx`, regardless if `pfx` is
> * a string literal known at compilation time or char * pointer known only at
> * runtime.
> */
> #define str_has_pfx(str, pfx) \
> (strncmp(str, pfx, __builtin_constant_p(pfx) ? sizeof(pfx) - 1
> : strlen(pfx)) == 0)
>
>
> > err = hashmap__add(map, name, 0);
> > if (err == -EEXIST)
> > --
> > 1.8.3.1
> >
--
Regards
Yafang
