linux-kernel - Re: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier

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Message-Id: <20171011170631.GN3521@linux.vnet.ibm.com>
Date:   Wed, 11 Oct 2017 10:06:31 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Howells <dhowells@...hat.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        torvalds@...ux-foundation.org, mark.rutland@....com,
        linux-arch@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Alexander Kuleshov <kuleshovmail@...il.com>, dvyukov@...gle.com
Subject: Re: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove
 smp_read_barrier_depends()

On Wed, Oct 11, 2017 at 06:54:05PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 11, 2017 at 09:47:48AM -0700, Paul E. McKenney wrote:
> > Interesting.  Do we currently have any dependencies headed by
> > this_cpu_read()?
> 
> Nope, but almost, look for: cpufreq_update_util_data.

This, you mean?

data = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_update_util_data));

True, a non-RCU dependency use case would want to use ACCESS_ONCE()
in the new regime.

							Thanx, Paul