linux-kernel - Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu

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Date:   Wed, 20 May 2020 20:35:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu@...r.kernel.org
Subject: Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu_data
 access

On Wed, May 20, 2020 at 08:28:00PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-05-20 13:42:59 [-0400], Joel Fernandes wrote:
> > Hi Sebastian,
> Hi Joel,
> 
> > For pointer stability, can we just use get_local_ptr() and put_local_ptr()
> > instead of adding an extra lock? This keeps the pointer stable while keeping
> > the section preemptible on -rt. And we already have a lock in rcu_data, I
> > prefer not to add another lock if possible.
> 
> What is this get_local_ptr() doing? I can't find it anywhere…

I suspect it is ({ preempt_disable(); this_cpu_ptr(ptr); }), or
something along those lines.

But yeah, I can't find it either.