netdev - Re: [PATCH bpf-next 0/4] Fix perf_buffer creation on systems with offline CPUs

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Message-ID: <CAEf4BzbEfuDNVr_gfEu13GvBAvdE1Qdw6nOxOJENzm69=iyUgg@mail.gmail.com>
Date:   Sun, 9 Feb 2020 10:32:43 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     Andrii Nakryiko <andriin@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>, bpf <bpf@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        linux- stable <stable@...r.kernel.org>,
        lkft-triage@...ts.linaro.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Leo Yan <leo.yan@...aro.org>
Subject: Re: [PATCH bpf-next 0/4] Fix perf_buffer creation on systems with
 offline CPUs

On Sun, Feb 9, 2020 at 9:18 AM Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>
> On Thu, 12 Dec 2019 at 07:05, Andrii Nakryiko <andriin@...com> wrote:
> >
> > This patch set fixes perf_buffer__new() behavior on systems which have some of
> > the CPUs offline/missing (due to difference between "possible" and "online"
> > sets). perf_buffer will create per-CPU buffer and open/attach to corresponding
> > perf_event only on CPUs present and online at the moment of perf_buffer
> > creation. Without this logic, perf_buffer creation has no chances of
> > succeeding on such systems, preventing valid and correct BPF applications from
> > starting.
> >
> > Andrii Nakryiko (4):
> >   libbpf: extract and generalize CPU mask parsing logic
> >   selftests/bpf: add CPU mask parsing tests
> >   libbpf: don't attach perf_buffer to offline/missing CPUs
>
> perf build failed on stable-rc 5.5 branch.
>
> libbpf.c: In function '__perf_buffer__new':
> libbpf.c:6159:8: error: implicit declaration of function
> 'parse_cpu_mask_file'; did you mean 'parse_uint_from_file'?
> [-Werror=implicit-function-declaration]
>   err = parse_cpu_mask_file(online_cpus_file, &online, &n);
>         ^~~~~~~~~~~~~~~~~~~
>         parse_uint_from_file
> libbpf.c:6159:8: error: nested extern declaration of
> 'parse_cpu_mask_file' [-Werror=nested-externs]
>
> build log,
> https://ci.linaro.org/view/lkft/job/openembedded-lkft-linux-stable-rc-5.5/DISTRO=lkft,MACHINE=hikey,label=docker-lkft/11/console
>

Thanks for reporting!

These changes depend on commit 6803ee25f0ea ("libbpf: Extract and
generalize CPU mask parsing logic"), which weren't backported to
stable. Greg, can you please pull that one as well? Thanks!

> --
> Linaro LKFT
> https://lkft.linaro.org