linux-kernel - Re: [PATCH v2 bpf-next 1/2] bpf: use dedicated bpf_trace_printk event instead of trace

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Date:   Fri, 10 Jul 2020 13:55:41 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/2] bpf: use dedicated bpf_trace_printk event
 instead of trace_printk()

On Fri, Jul 10, 2020 at 7:25 AM Alan Maguire <alan.maguire@...cle.com> wrote:
>
> The bpf helper bpf_trace_printk() uses trace_printk() under the hood.
> This leads to an alarming warning message originating from trace
> buffer allocation which occurs the first time a program using
> bpf_trace_printk() is loaded.
>
> We can instead create a trace event for bpf_trace_printk() and enable
> it in-kernel when/if we encounter a program using the
> bpf_trace_printk() helper.  With this approach, trace_printk()
> is not used directly and no warning message appears.
>
> This work was started by Steven (see Link) and finished by Alan; added
> Steven's Signed-off-by with his permission.
>
> Link: https://lore.kernel.org/r/20200628194334.6238b933@oasis.local.home
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andriin@...com>

>  kernel/trace/Makefile    |  2 ++
>  kernel/trace/bpf_trace.c | 41 ++++++++++++++++++++++++++++++++++++-----
>  kernel/trace/bpf_trace.h | 34 ++++++++++++++++++++++++++++++++++
>  3 files changed, 72 insertions(+), 5 deletions(-)
>  create mode 100644 kernel/trace/bpf_trace.h
>

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