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Date:   Mon, 17 Jun 2019 19:09:20 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andriin@fb.com>, Yonghong Song <yhs@fb.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        Matt Mullins <mmullins@fb.com>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf: hide do_bpf_send_signal when unused
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On Mon, 17 Jun 2019 08:26:29 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Mon, Jun 17, 2019 at 5:59 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > When CONFIG_MODULES is disabled, this function is never called:
> >
> > kernel/trace/bpf_trace.c:581:13: error: 'do_bpf_send_signal' defined but not used [-Werror=unused-function]  
> 
> hmm. it should work just fine without modules.
> the bug is somewhere else.

>From what I see, the only use of do_bpf_send_signal is within a
#ifdef CONFIG_MODULES, which means that you will get a warning about a
static unused when CONFIG_MODULES is not defined.

In kernel/trace/bpf_trace.c we have:

static void do_bpf_send_signal(struct irq_work *entry)

[..]

#ifdef CONFIG_MODULES

[..]

        for_each_possible_cpu(cpu) {
                work = per_cpu_ptr(&send_signal_work, cpu);
                init_irq_work(&work->irq_work, do_bpf_send_signal);  <-- on use of do_bpf_send_signal
        }
[..]
#endif /* CONFIG_MODULES */

The bug (really just a warning) reported is exactly here.

-- Steve