linux-kernel - [PATCH bpf-next 10/11] samples: bpf: fix -Wsequence-point

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Date:   Thu, 14 Apr 2022 22:47:06 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     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>,
        Alexander Lobakin <alobakin@...me>,
        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, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH bpf-next 10/11] samples: bpf: fix -Wsequence-point

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>
---
 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