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

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Message-ID: <CALOAHbDtqpkN4D0vHvGxTSpQkksMWtFm3faMy0n+pazxN_RPPg@mail.gmail.com>
Date:   Mon, 29 Nov 2021 21:41:11 +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 6:13 PM Sven Schnelle <svens@...ux.ibm.com> wrote:
>
> Hi,
>
> Yafang Shao <laoar.shao@...il.com> writes:
>
> > As the sched:sched_switch tracepoint args are derived from the kernel,
> > we'd better make it same with the kernel. So the macro TASK_COMM_LEN is
> > converted to type enum, then all the BPF programs can get it through BTF.
> >
> > The BPF program which wants to use TASK_COMM_LEN should include the header
> > vmlinux.h. Regarding the test_stacktrace_map and test_tracepoint, as the
> > type defined in linux/bpf.h are also defined in vmlinux.h, so we don't
> > need to include linux/bpf.h again.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Acked-by: Andrii Nakryiko <andrii@...nel.org>
> > Acked-by: David Hildenbrand <david@...hat.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: Michal Miroslaw <mirq-linux@...e.qmqm.pl>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Matthew Wilcox <willy@...radead.org>
> > Cc: David Hildenbrand <david@...hat.com>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Petr Mladek <pmladek@...e.com>
> > ---
> >  include/linux/sched.h                                   | 9 +++++++--
> >  tools/testing/selftests/bpf/progs/test_stacktrace_map.c | 6 +++---
> >  tools/testing/selftests/bpf/progs/test_tracepoint.c     | 6 +++---
> >  3 files changed, 13 insertions(+), 8 deletions(-)
> >
> > 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,
 };

-- 
Thanks
Yafang