netdev - Re: [PATCH v2 7/7] tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM

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Date:   Mon, 29 Nov 2021 23:28:55 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Sven Schnelle <svens@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel test robot <oliver.sang@...el.com>,
        kbuild test robot <lkp@...el.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v2 7/7] tools/testing/selftests/bpf: replace open-coded 16
 with TASK_COMM_LEN

On Mon, Nov 29, 2021 at 10:21 PM Sven Schnelle <svens@...ux.ibm.com> wrote:
>
> Hi,
>
> Yafang Shao <laoar.shao@...il.com> writes:
>
> > On Mon, Nov 29, 2021 at 6:13 PM Sven Schnelle <svens@...ux.ibm.com> wrote:
> >> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> >> > index 78c351e35fec..cecd4806edc6 100644
> >> > --- a/include/linux/sched.h
> >> > +++ b/include/linux/sched.h
> >> > @@ -274,8 +274,13 @@ struct task_group;
> >> >
> >> >  #define get_current_state()  READ_ONCE(current->__state)
> >> >
> >> > -/* Task command name length: */
> >> > -#define TASK_COMM_LEN                        16
> >> > +/*
> >> > + * Define the task command name length as enum, then it can be visible to
> >> > + * BPF programs.
> >> > + */
> >> > +enum {
> >> > +     TASK_COMM_LEN = 16,
> >> > +};
> >>
> >> This breaks the trigger-field-variable-support.tc from the ftrace test
> >> suite at least on s390:
> >>
> >> echo
> >> 'hist:keys=next_comm:wakeup_lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,next_pid,sched.sched_waking.prio,next_comm)
> >> if next_comm=="ping"'
> >> linux/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-field-variable-support.tc: line 15: echo: write error: Invalid argument
> >>
> >> I added a debugging line into check_synth_field():
> >>
> >> [   44.091037] field->size 16, hist_field->size 16, field->is_signed 1, hist_field->is_signed 0
> >>
> >> Note the difference in the signed field.
> >>
> >
> > Hi Sven,
> >
> > Thanks for the report and debugging!
> > Seems we should explicitly define it as signed ?
> > Could you pls. help verify it?
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index cecd4806edc6..44d36c6af3e1 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -278,7 +278,7 @@ struct task_group;
> >   * Define the task command name length as enum, then it can be visible to
> >   * BPF programs.
> >   */
> > -enum {
> > +enum SignedEnum {
> >         TASK_COMM_LEN = 16,
> >  };
>
> Umm no. What you're doing here is to define the name of the enum as
> 'SignedEnum'. This doesn't change the type. I think before C++0x you
> couldn't force an enum type.
>

Ah, I made a stupid mistake....


-- 
Thanks
Yafang