linux-kernel - Re: [PATCH v3 10/25] openrisc: add spinlock implementation

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Message-ID: <20170222120849.GR6536@twins.programming.kicks-ass.net>
Date:   Wed, 22 Feb 2017 13:08:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Stafford Horne <shorne@...il.com>
Cc:     Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        linux@...ck-us.net, openrisc@...ts.librecores.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3 10/25] openrisc: add spinlock implementation

On Wed, Feb 22, 2017 at 12:41:17PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 22, 2017 at 04:11:39AM +0900, Stafford Horne wrote:
> > +static inline void arch_spin_unlock(arch_spinlock_t *lock)
> > +{
> > +	smp_mb();
> > +	lock->tickets.owner++;
> > +}
> 
> This is putting a lot of trust in the compiler, nothing is volatile so
> it can do horrible things.

Also, your architecture manual seems to not explicitly mention how
l.lwa/l.swa interact with overlapping l.sh.

In fact, I can read the text such that its done 'wrong'.