linux-kernel - Re: [PATCH bpf-next v2 2/3] selftests/bpf: skip recursive functions for kprobe

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Message-ID: <CALC8CXdNYGy2itPVkmuS3grfCof9ggHTRVyps85_9X2WwREpXQ@mail.gmail.com>
Date: Thu, 2 Oct 2025 12:18:11 -0400
From: ChaosEsque Team <chaosesqueteam@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: andrii@...nel.org, eddyz87@...il.com, mykolal@...com, ast@...nel.org, 
	daniel@...earbox.net, martin.lau@...ux.dev, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, shuah@...nel.org, 
	yikai.lin@...o.com, memxor@...il.com, bpf@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 2/3] selftests/bpf: skip recursive functions
 for kprobe_multi

Indeed, it is so long. Sir Dong, of Meng.

On Tue, Aug 26, 2025 at 4:05 AM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> Some functions is recursive for the kprobe_multi and impact the benchmark
> results. So just skip them.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v2:
> - introduce trace_blacklist instead of copy-pasting strcmp
> ---
>  tools/testing/selftests/bpf/trace_helpers.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
> index d24baf244d1f..9577979bd84d 100644
> --- a/tools/testing/selftests/bpf/trace_helpers.c
> +++ b/tools/testing/selftests/bpf/trace_helpers.c
> @@ -19,6 +19,7 @@
>  #include <gelf.h>
>  #include "bpf/hashmap.h"
>  #include "bpf/libbpf_internal.h"
> +#include "bpf_util.h"
>
>  #define TRACEFS_PIPE   "/sys/kernel/tracing/trace_pipe"
>  #define DEBUGFS_PIPE   "/sys/kernel/debug/tracing/trace_pipe"
> @@ -540,8 +541,20 @@ static bool is_invalid_entry(char *buf, bool kernel)
>         return false;
>  }
>
> +static const char * const trace_blacklist[] = {
> +       "migrate_disable",
> +       "migrate_enable",
> +       "rcu_read_unlock_strict",
> +       "preempt_count_add",
> +       "preempt_count_sub",
> +       "__rcu_read_lock",
> +       "__rcu_read_unlock",
> +};
> +
>  static bool skip_entry(char *name)
>  {
> +       int i;
> +
>         /*
>          * We attach to almost all kernel functions and some of them
>          * will cause 'suspicious RCU usage' when fprobe is attached
> @@ -559,6 +572,12 @@ static bool skip_entry(char *name)
>         if (!strncmp(name, "__ftrace_invalid_address__",
>                      sizeof("__ftrace_invalid_address__") - 1))
>                 return true;
> +
> +       for (i = 0; i < ARRAY_SIZE(trace_blacklist); i++) {
> +               if (!strcmp(name, trace_blacklist[i]))
> +                       return true;
> +       }
> +
>         return false;
>  }
>
> --
> 2.51.0
>
>