linux-kernel - Re: [PATCH bpf-next 2/3] uprobes: prepare uprobe args buffer lazily

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Message-ID: <CAEf4BzYFzLuGB93digNwCnHZ=LEjxvyfPb4GcF3Mwqi-JP3skw@mail.gmail.com>
Date: Wed, 13 Mar 2024 09:57:08 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, linux-trace-kernel@...r.kernel.org, 
	rostedt@...dmis.org, mhiramat@...nel.org, bpf@...r.kernel.org, 
	mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/3] uprobes: prepare uprobe args buffer lazily

On Wed, Mar 13, 2024 at 8:48 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> Again, looks good to me, but I have a minor nit. Feel free to ignore.
>
> On 03/12, Andrii Nakryiko wrote:
> >
> >  static void __uprobe_trace_func(struct trace_uprobe *tu,
> >                               unsigned long func, struct pt_regs *regs,
> > -                             struct uprobe_cpu_buffer *ucb,
> > +                             struct uprobe_cpu_buffer **ucbp,
> >                               struct trace_event_file *trace_file)
> >  {
> >       struct uprobe_trace_entry_head *entry;
> >       struct trace_event_buffer fbuffer;
> > +     struct uprobe_cpu_buffer *ucb;
> >       void *data;
> >       int size, esize;
> >       struct trace_event_call *call = trace_probe_event_call(&tu->tp);
> >
> > +     ucb = *ucbp;
> > +     if (!ucb) {
> > +             ucb = prepare_uprobe_buffer(tu, regs);
> > +             *ucbp = ucb;
> > +     }
>
> perhaps it would be more clean to pass ucbp to prepare_uprobe_buffer()
> and change it to do
>
>         if (*ucbp)
>                 return *ucbp;
>
> at the start. Then __uprobe_trace_func() and __uprobe_perf_func() can
> simply do
>
>         ucb = prepare_uprobe_buffer(tu, regs, ucbp);

ok, will do

>
> > -     uprobe_buffer_put(ucb);
> > +     if (ucb)
> > +             uprobe_buffer_put(ucb);
>
> Similarly, I think the "ucb != NULL" check should be shifted into
> uprobe_buffer_put().

sure, will hide it inside uprobe_buffer_put()

>
> Oleg.
>