Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 20 May 2020 20:35:29 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Joel Fernandes <joel@joelfernandes.org>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Will Deacon <will@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        rcu@vger.kernel.org
Subject: Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu_data
 access
Message-ID: <20200520183529.GR317569@hirez.programming.kicks-ass.net>
References: <20200519201912.1564477-1-bigeasy@linutronix.de>
 <20200519201912.1564477-4-bigeasy@linutronix.de>
 <20200520102407.GF317569@hirez.programming.kicks-ass.net>
 <20200520120608.mwros5jurmidxxfv@linutronix.de>
 <20200520174259.GA247557@google.com>
 <20200520182800.sdp6t6bgbhn4kkqk@linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20200520182800.sdp6t6bgbhn4kkqk@linutronix.de>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.