From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>
Subject: Re: [RFC bpf-next 4/4] selftests/bpf: Add attach bench test
Date: Tue, 12 Apr 2022 15:51:43 -0700 [thread overview]
Message-ID: <CAEf4BzaQRcZGMqq5wqHo3wSHZAAVvY6AhizDk_dV_GtnwHuxLQ@mail.gmail.com> (raw)
In-Reply-To: <20220412094923.0abe90955e5db486b7bca279@kernel.org>
On Mon, Apr 11, 2022 at 5:49 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Mon, 11 Apr 2022 15:15:40 -0700
> Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>
> > > +#define DEBUGFS "/sys/kernel/debug/tracing/"
> > > +
> > > +static int get_syms(char ***symsp, size_t *cntp)
> > > +{
> > > + size_t cap = 0, cnt = 0, i;
> > > + char *name, **syms = NULL;
> > > + struct hashmap *map;
> > > + char buf[256];
> > > + FILE *f;
> > > + int err;
> > > +
> > > + /*
> > > + * The available_filter_functions contains many duplicates,
> > > + * but other than that all symbols are usable in kprobe multi
> > > + * interface.
> > > + * Filtering out duplicates by using hashmap__add, which won't
> > > + * add existing entry.
> > > + */
> > > + f = fopen(DEBUGFS "available_filter_functions", "r");
> >
> > I'm really curious how did you manage to attach to everything in
> > available_filter_functions because when I'm trying to do that I fail.
> > available_filter_functions has a bunch of functions that should not be
> > attachable (e.g., notrace functions). Look just at __bpf_tramp_exit:
> >
> > void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr);
>
> Hmm, this sounds like a bug in ftrace side. IIUC, the
> "available_filter_functions" only shows the functions which is NOT
> instrumented by mcount, we should not see any notrace functions on it.
>
> Technically, this is done by __no_instrument_function__ attribute.
>
> #if defined(CC_USING_HOTPATCH)
> #define notrace __attribute__((hotpatch(0, 0)))
> #elif defined(CC_USING_PATCHABLE_FUNCTION_ENTRY)
> #define notrace __attribute__((patchable_function_entry(0, 0)))
> #else
> #define notrace __attribute__((__no_instrument_function__))
> #endif
>
> >
> > So first, curious what I am doing wrong or rather why it succeeds in
> > your case ;)
> >
> > But second, just wanted to plea to "fix" available_filter_functions to
> > not list stuff that should not be attachable. Can you please take a
> > look and checks what's going on there and why do we have notrace
> > functions (and what else should *NOT* be there)?
>
> Can you share how did you reproduce the issue? I'll check it.
>
$ sudo cat /sys/kernel/debug/tracing/available_filter_functions | grep
__bpf_tramp
__bpf_tramp_image_release
__bpf_tramp_image_put_rcu_tasks
__bpf_tramp_image_put_rcu
__bpf_tramp_image_put_deferred
__bpf_tramp_exit
__bpf_tramp_exit is notrace function, so shouldn't be here. Notice
that __bpf_tramp_enter (which is also notrace) are not in
available_filter_functions.
So it's quite bizarre and inconsistent.
> Thank you,
>
>
> --
> Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2022-04-12 23:20 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-07 12:52 [RFC bpf-next 0/4] bpf: Speed up symbol resolving in kprobe multi link Jiri Olsa
2022-04-07 12:52 ` [RFC bpf-next 1/4] kallsyms: Add kallsyms_lookup_names function Jiri Olsa
2022-04-08 0:57 ` Masami Hiramatsu
2022-04-13 7:27 ` Jiri Olsa
2022-04-08 23:19 ` Alexei Starovoitov
2022-04-09 20:24 ` Jiri Olsa
2022-04-12 20:46 ` Jiri Olsa
2022-04-15 0:47 ` Masami Hiramatsu
2022-04-15 22:39 ` Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-12 20:28 ` Jiri Olsa
2022-04-07 12:52 ` [RFC bpf-next 2/4] fprobe: Resolve symbols with kallsyms_lookup_names Jiri Olsa
2022-04-08 0:58 ` Masami Hiramatsu
2022-04-07 12:52 ` [RFC bpf-next 3/4] bpf: Resolve symbols with kallsyms_lookup_names for kprobe multi link Jiri Olsa
2022-04-08 23:26 ` Alexei Starovoitov
2022-04-09 20:24 ` Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-12 18:42 ` Jiri Olsa
2022-04-07 12:52 ` [RFC bpf-next 4/4] selftests/bpf: Add attach bench test Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-12 0:49 ` Masami Hiramatsu
2022-04-12 22:51 ` Andrii Nakryiko [this message]
2022-04-16 14:21 ` Masami Hiramatsu
2022-04-18 17:33 ` Steven Rostedt
2022-04-28 13:58 ` Steven Rostedt
2022-04-28 13:59 ` Steven Rostedt
2022-04-28 18:59 ` Alexei Starovoitov
2022-04-28 20:05 ` Steven Rostedt
2022-04-28 23:32 ` Andrii Nakryiko
2022-04-28 23:53 ` Steven Rostedt
2022-04-29 0:09 ` Steven Rostedt
2022-04-29 0:31 ` Steven Rostedt
2022-04-13 16:44 ` Steven Rostedt
2022-04-13 16:45 ` Andrii Nakryiko
2022-04-13 16:59 ` Steven Rostedt
2022-04-13 19:02 ` Andrii Nakryiko
2022-04-12 15:44 ` Jiri Olsa
2022-04-12 22:59 ` Andrii Nakryiko
2022-04-08 23:29 ` [RFC bpf-next 0/4] bpf: Speed up symbol resolving in kprobe multi link Alexei Starovoitov
2022-04-09 20:24 ` Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-11 22:18 ` Alexei Starovoitov
2022-04-11 22:21 ` Andrii Nakryiko
2022-04-12 15:46 ` Jiri Olsa
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