linux-kernel - Re: [PATCH] bpf: hide do_bpf_send

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Message-ID: <07dafa45-4141-2559-43ae-a0c80624426b@fb.com>
Date:   Mon, 24 Jun 2019 20:37:50 +0000
From:   Yonghong Song <yhs@...com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        "arnd@...db.de" <arnd@...db.de>
CC:     Matt Mullins <mmullins@...com>, Song Liu <songliubraving@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Martin Lau" <kafai@...com>, Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH] bpf: hide do_bpf_send_signal when unused



On 6/17/19 5:18 PM, Steven Rostedt wrote:
> On Mon, 17 Jun 2019 16:27:33 -0700
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> 
>> On Mon, Jun 17, 2019 at 4:13 PM Matt Mullins <mmullins@...com> wrote:
>>>>
>>>> The bug (really just a warning) reported is exactly here.
>>>
>>> I don't think bpf_send_signal is tied to modules at all;
>>> send_signal_irq_work_init and the corresponding initcall should be
>>> moved outside that #ifdef.
>>
>> right. I guess send_signal_irq_work_init was accidentally placed
>> after bpf_event_init and happened to be within that ifdef.
>> Should definitely be outside.
> 
> So Arnd did find a bug. Just the wrong solution ;-)
> 
> -- Steve

Hi, Arnd,

The following change can fix the issue.

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index c102c240bb0b..ca1255d14576 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1431,6 +1431,20 @@ int bpf_get_perf_event_info(const struct 
perf_event *event, u32 *prog_id,
         return err;
  }

+static int __init send_signal_irq_work_init(void)
+{
+       int cpu;
+       struct send_signal_irq_work *work;
+
+       for_each_possible_cpu(cpu) {
+               work = per_cpu_ptr(&send_signal_work, cpu);
+               init_irq_work(&work->irq_work, do_bpf_send_signal);
+       }
+       return 0;
+}
+
+subsys_initcall(send_signal_irq_work_init);
+
  #ifdef CONFIG_MODULES
  static int bpf_event_notify(struct notifier_block *nb, unsigned long op,
                             void *module)
@@ -1478,18 +1492,5 @@ static int __init bpf_event_init(void)
         return 0;
  }

-static int __init send_signal_irq_work_init(void)
-{
-       int cpu;
-       struct send_signal_irq_work *work;
-
-       for_each_possible_cpu(cpu) {
-               work = per_cpu_ptr(&send_signal_work, cpu);
-               init_irq_work(&work->irq_work, do_bpf_send_signal);
-       }
-       return 0;
-}
-
  fs_initcall(bpf_event_init);
-subsys_initcall(send_signal_irq_work_init);
  #endif /* CONFIG_MODULES */

Could you submit a new revision? Thanks!

Yonghong