linux-kernel - Re: [PATCH v2 rcu/dev 2/2] rcu: Disable laziness if lazy-tracking says so

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Message-ID: <CAEXW_YRjV0CqoALU6F_9LZKD_e84gWQ3a8juucmXxLUuDQ7DHw@mail.gmail.com>
Date:   Sun, 15 Jan 2023 16:29:38 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        fweisbec@...il.com, urezki@...il.com
Subject: Re: [PATCH v2 rcu/dev 2/2] rcu: Disable laziness if lazy-tracking
 says so

On Sun, Jan 15, 2023 at 3:55 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Thu, 12 Jan 2023 00:52:23 +0000
> "Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:
>
> >
> >  static void
> > -__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> > +__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
> >  {
> >       static atomic_t doublefrees;
> >       unsigned long flags;
> >       struct rcu_data *rdp;
> > -     bool was_alldone;
> > +     bool was_alldone, lazy;
>
> I'm curious to why the the extra variable.
>
> >
> >       /* Misaligned rcu_head! */
> >       WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
> > @@ -2622,6 +2622,7 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> >       kasan_record_aux_stack_noalloc(head);
> >       local_irq_save(flags);
> >       rdp = this_cpu_ptr(&rcu_data);
> > +     lazy = lazy_in && !rcu_async_should_hurry();
>
> Wouldn't just having:
>
>         lazy = lazy && !rcu_async_should_hurry();
>
> be sufficient?

I prefer to not overwrite function arguments, it makes debugging harder IMHO.

 - Joel



>
> -- Steve
>
> >
> >       /* Add the callback to our list. */
> >       if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
> > --