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

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Message-ID: <CAEf4BzaHFPpz9QmVNOHH_hJ-KOF+wsimGqBYRnNwAhz7zcj35w@mail.gmail.com>
Date: Tue, 20 May 2025 13:30:51 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, 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 Tue, May 20, 2025 at 1:08 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> 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.
>

yep, my bad, missed find_vpid() restrictions. revert LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

> Jiri ?