netdev - Re: [PATCH bpf-next v5 11/12] bpf: selftests: Fix fd cleanup in get_branch

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Date:   Tue, 28 Sep 2021 23:58:10 +0000
From:   Song Liu <songliubraving@...com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
CC:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "Martin Lau" <kafai@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 11/12] bpf: selftests: Fix fd cleanup in
 get_branch_snapshot



> On Sep 27, 2021, at 7:59 AM, Kumar Kartikeya Dwivedi <memxor@...il.com> wrote:
> 
> Cleanup code uses while (cpu++ < cpu_cnt) for closing fds, which means
> it starts iterating from 1 for closing fds. If the first fd is -1, it
> skips over it and closes garbage fds (typically zero) in the remaining
> array. This leads to test failures for future tests when they end up
> storing fd 0 (as the slot becomes free due to close(0)) in ldimm64's BTF
> fd, ending up trying to match module BTF id with vmlinux.
> 
> This was observed as spurious CI failure for the ksym_module_libbpf and
> module_attach tests. The test ends up closing fd 0 and breaking libbpf's
> assumption that module BTF fd will always be > 0, which leads to the
> kernel thinking that we are pointing to a BTF ID in vmlinux BTF.
> 
> Cc: Song Liu <songliubraving@...com>
> Fixes: 025bd7c753aa (selftests/bpf: Add test for bpf_get_branch_snapshot)
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>

Thanks for the fix!

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

> ---
> tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> index f81db9135ae4..67e86f8d8677 100644
> --- a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> +++ b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
> @@ -38,10 +38,9 @@ static int create_perf_events(void)
> 
> static void close_perf_events(void)
> {
> -	int cpu = 0;
> -	int fd;
> +	int cpu, fd;
> 
> -	while (cpu++ < cpu_cnt) {
> +	for (cpu = 0; cpu < cpu_cnt; cpu++) {
> 		fd = pfd_array[cpu];
> 		if (fd < 0)
> 			break;
> -- 
> 2.33.0
>