linux-kernel - Re: [PATCH -mm 5/5] bpf/progs: replace hard-coded 16 with TASK_COMM

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Message-ID: <CALOAHbBv-_5uF=T4MyC_6J08PRX6KTGora4FArdYKLC0dOy8HQ@mail.gmail.com>
Date:   Sun, 5 Dec 2021 15:25:27 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        David Hildenbrand <david@...hat.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        linux-mm <linux-mm@...ck.org>, bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH -mm 5/5] bpf/progs: replace hard-coded 16 with TASK_COMM_LEN

On Sun, Dec 5, 2021 at 11:13 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sat, Dec 4, 2021 at 6:45 PM Yafang Shao <laoar.shao@...il.com> wrote:
> >
> > On Sun, Dec 5, 2021 at 12:44 AM Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:
> > >
> > > On Sat, Dec 4, 2021 at 1:53 AM Yafang Shao <laoar.shao@...il.com> wrote:
> > > >
> > > >  static int process_sample(void *ctx, void *data, size_t len)
> > > >  {
> > > > -       struct sample *s = data;
> > > > +       struct sample_ringbuf *s = data;
> > >
> > > This is becoming pointless churn.
> > > Nack.
> > >
> > > > index 145028b52ad8..7b1bb73c3501 100644
> > > > --- a/tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c
> > > > +++ b/tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c
> > > > @@ -1,8 +1,7 @@
> > > >  // SPDX-License-Identifier: GPL-2.0
> > > >  // Copyright (c) 2019 Facebook
> > > >
> > > > -#include <linux/bpf.h>
> > > > -#include <stdint.h>
> > > > +#include <vmlinux.h>
> > > >  #include <stdbool.h>
> > > >  #include <bpf/bpf_helpers.h>
> > > >  #include <bpf/bpf_core_read.h>
> > > > @@ -23,11 +22,11 @@ struct core_reloc_kernel_output {
> > > >         int comm_len;
> > > >  };
> > > >
> > > > -struct task_struct {
> > > > +struct task_struct_reloc {
> > >
> > > Churn that is not even compile tested.
> >
> > It is strange that I have successfully compiled it....
> > Below is the compile log,
> >
> > $ cat make.log | grep test_core_reloc_kernel
> >   CLNG-BPF [test_maps] test_core_reloc_kernel.o
> >   GEN-SKEL [test_progs] test_core_reloc_kernel.skel.h
> >   CLNG-BPF [test_maps] test_core_reloc_kernel.o
> >   GEN-SKEL [test_progs-no_alu32] test_core_reloc_kernel.skel.h
> >
> > Also there's no error in the compile log.
>
> and ran the tests too?

My bad. I thought it was just a name change, which will work well if
it can be compiled successfully.
But it seems the task_struct in this file is a dummy struct, which
will be relocated to the real task_struct defined in the kernel.
We can't include vmlinux.h in this file, as it is for the relocation test.

-- 
Thanks
Yafang