Subject: Re: [PATCHv2 bpf 3/3] bpf: Force cookies array to follow symbols sorting

From: Jiri Olsa <[email-masked]>
Date: Tue, 7 Jun 2022 21:55:58 +0200

On Tue, Jun 07, 2022 at 11:40:47AM -0700, Alexei Starovoitov wrote:
> On Mon, Jun 6, 2022 at 11:48 AM Jiri Olsa <[email-masked]> 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 <[email-masked]>
> 
> 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

looks like kallsyms search failed to find some symbol,
but I can't reproduce with:

  ./vmtest.sh -- ./test_progs -t kprobe_multi

can you share .config you used?

thanks,
jirka

> 
> 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