netdev - Re: [PATCH bpf-next 10/11] samples: bpf: fix -Wsequence-point

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Date:   Fri, 15 Apr 2022 16:56:25 -0700
From:   Song Liu <song@...nel.org>
To:     Alexander Lobakin <alobakin@...me>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dmitrii Dolgov <9erthalion6@...il.com>,
        Quentin Monnet <quentin@...valent.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Chenbo Feng <fengc@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Daniel Wagner <daniel.wagner@...-carit.de>,
        Thomas Graf <tgraf@...g.ch>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        linux-perf-users@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH bpf-next 10/11] samples: bpf: fix -Wsequence-point

On Thu, Apr 14, 2022 at 3:47 PM Alexander Lobakin <alobakin@...me> wrote:
>
> In some libc implementations, CPU_SET() may utilize its first
> argument several times. When combined with a post-increment, it
> leads to:
>
> samples/bpf/test_lru_dist.c:233:36: warning: operation on 'next_to_try' may be undefined [-Wsequence-point]
>   233 |                 CPU_SET(next_to_try++, &cpuset);
>       |                                    ^
>
> Split the sentence into two standalone operations to fix this.
>
> Fixes: 5db58faf989f ("bpf: Add tests for the LRU bpf_htab")
> Signed-off-by: Alexander Lobakin <alobakin@...me>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  samples/bpf/test_lru_dist.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/samples/bpf/test_lru_dist.c b/samples/bpf/test_lru_dist.c
> index be98ccb4952f..191643ec501e 100644
> --- a/samples/bpf/test_lru_dist.c
> +++ b/samples/bpf/test_lru_dist.c
> @@ -229,7 +229,8 @@ static int sched_next_online(int pid, int next_to_try)
>
>         while (next_to_try < nr_cpus) {
>                 CPU_ZERO(&cpuset);
> -               CPU_SET(next_to_try++, &cpuset);
> +               CPU_SET(next_to_try, &cpuset);
> +               next_to_try++;
>                 if (!sched_setaffinity(pid, sizeof(cpuset), &cpuset))
>                         break;
>         }
> --
> 2.35.2
>
>