linux-kernel - Re: [PATCH] Revert "bpf: remove unnecessary rcu_read_{lock,unlock}() in multi-uprobe attach logic"

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Message-ID: <CAADnVQKZti=SXM=4owtk9jEqGMcD0mUqb46PNYwhquYfyORUuw@mail.gmail.com>
Date: Tue, 20 May 2025 13:07:59 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: Song Liu <song@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Steven Rostedt <rostedt@...dmis.org>, Alexei Starovoitov <ast@...nel.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, xuewen.yan94@...il.com, 
	di.shen@...soc.com
Subject: Re: [PATCH] Revert "bpf: remove unnecessary rcu_read_{lock,unlock}()
 in multi-uprobe attach logic"

On Mon, May 19, 2025 at 10:51 PM Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> From: Di Shen <di.shen@...soc.com>
>
> This reverts commit 4a8f635a60540888dab3804992e86410360339c8.
>
> Althought get_pid_task() internally already calls rcu_read_lock() and
> rcu_read_unlock(), the find_vpid() was not.
>
> The documentation for find_vpid() clearly states:
>
>   "Must be called with the tasklist_lock or rcu_read_lock() held."
>
> Add proper rcu_read_lock/unlock() to protect the find_vpid().
>
> Reported-by: Xuewen Yan <xuewen.yan@...soc.com>
> Signed-off-by: Di Shen <di.shen@...soc.com>
> ---
>  kernel/trace/bpf_trace.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 187dc37d61d4..0c4b6af10601 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3417,7 +3417,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>         }
>
>         if (pid) {
> +               rcu_read_lock();
>                 task = get_pid_task(find_vpid(pid), PIDTYPE_TGID);
> +               rcu_read_unlock();
>                 if (!task) {
>                         err = -ESRCH;
>                         goto error_path_put;

hmm. indeed.

Jiri ?