linux-kernel - Re: [PATCHv2 bpf 3/3] bpf: Force cookies array to follow symbols sorting

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Message-ID: <CAADnVQJA54Ra8+tV0e0KwSXAg93JRoiefDXWR-Lqatya5YWKpg@mail.gmail.com>
Date:   Tue, 7 Jun 2022 11:40:47 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCHv2 bpf 3/3] bpf: Force cookies array to follow symbols sorting

On Mon, Jun 6, 2022 at 11:48 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> When user specifies symbols and cookies for kprobe_multi link
> interface it's very likely the cookies will be misplaced and
> returned to wrong functions (via get_attach_cookie helper).
>
> The reason is that to resolve the provided functions we sort
> them before passing them to ftrace_lookup_symbols, but we do
> not do the same sort on the cookie values.
>
> Fixing this by using sort_r function with custom swap callback
> that swaps cookie values as well.
>
> Fixes: 0236fec57a15 ("bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link")
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>

It looks good, but something in this patch is causing a regression:
./test_progs -t kprobe_multi
test_kprobe_multi_test:PASS:load_kallsyms 0 nsec
#80/1    kprobe_multi_test/skel_api:OK
#80/2    kprobe_multi_test/link_api_addrs:OK
#80/3    kprobe_multi_test/link_api_syms:OK
#80/4    kprobe_multi_test/attach_api_pattern:OK
#80/5    kprobe_multi_test/attach_api_addrs:OK
#80/6    kprobe_multi_test/attach_api_syms:OK
#80/7    kprobe_multi_test/attach_api_fails:OK
test_bench_attach:PASS:get_syms 0 nsec
test_bench_attach:PASS:kprobe_multi_empty__open_and_load 0 nsec
libbpf: prog 'test_kprobe_empty': failed to attach: No such process
test_bench_attach:FAIL:bpf_program__attach_kprobe_multi_opts
unexpected error: -3
#80/8    kprobe_multi_test/bench_attach:FAIL
#80      kprobe_multi_test:FAIL

CI is unfortunately green, because we don't run it there:
#80/1 kprobe_multi_test/skel_api:OK
#80/2 kprobe_multi_test/link_api_addrs:OK
#80/3 kprobe_multi_test/link_api_syms:OK
#80/4 kprobe_multi_test/attach_api_pattern:OK
#80/5 kprobe_multi_test/attach_api_addrs:OK
#80/6 kprobe_multi_test/attach_api_syms:OK
#80/7 kprobe_multi_test/attach_api_fails:OK
#80 kprobe_multi_test:OK