linux-kernel - Re: [for-next][PATCH 13/25] x86/mm/kmmio: Use rcu_read_lock_sched

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Message-ID: <20221210213412.GF4001@paulmck-ThinkPad-P17-Gen-1>
Date:   Sat, 10 Dec 2022 13:34:12 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Karol Herbst <karolherbst@...il.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [for-next][PATCH 13/25] x86/mm/kmmio: Use
 rcu_read_lock_sched_notrace()

On Sat, Dec 10, 2022 at 01:34:25PM -0500, Steven Rostedt wrote:
> On Sat, 10 Dec 2022 09:47:53 -0800
> "Paul E. McKenney" <paulmck@...nel.org> wrote:
> 
> > > Note, the preempt_disable() is still needed as it uses preempt_enable_no_resched().
> > > 
> 
>  ...
> 
> > Executable code can be the best form of comment.  ;-)
> > 
> > This does mess with preempt_count() redundantly, but the overhead from
> > that should be way down in the noise.
> 
> I was going to remove it, but then I realized that it would be a functional
> change, as from the comment above, it uses "preempt_enable_no_resched(),
> which there is not a rcu_read_unlock_sched() variant.

If this happens often enough, it might be worth adding something like
rcu_read_unlock_sched_no_resched(), but we clearly are not there yet.
Especially not with a name like that!  ;-)

							Thanx, Paul

> > Acked-by: Paul E. McKenney <paulmck@...nel.org>
> 
> Thanks! I'll add this to the commit.
> 
> -- Steve