linux-kernel - Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire

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Message-ID: <20180712180511.GP2476@hirez.programming.kicks-ass.net>
Date:   Thu, 12 Jul 2018 20:05:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Will Deacon <will.deacon@....com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire

On Thu, Jul 12, 2018 at 10:28:38AM -0700, Paul E. McKenney wrote:
> Look for the uses of raw_spin_lock_irq_rcu_node() and friends in
> kernel/rcu and include/linux/*rcu*, along with the explanation in
> Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
> 
> I must confess that I am not following exactly what Peter is calling
> out as the failure.  My best guess is that he is leading up to his
> call for RCsc locks, but I might have missed a turn.

Yes, it is part of my call for RCsc locks.

The locking pattern is fairly simple and shows where RCpc comes apart
from expectation real nice.

Yes I helped clean up the barrier usage, but as always it'd be even
cleaner if we could just do away with the special barrier entirely.