linux-kernel - Re: [PATCH 1/2] lib: Provide generic atomic64

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Message-ID: <19002.57382.880505.913539@cargo.ozlabs.ibm.com>
Date:	Fri, 19 Jun 2009 10:47:34 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	benh@...nel.crashing.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lib: Provide generic atomic64_t implementation

Mike Frysinger writes:

> On Sat, Jun 13, 2009 at 03:10, Paul Mackerras wrote:
> > +typedef struct {
> > +       long long counter;
> > +} atomic64_t;
> 
> lack of volatile seems odd compared to:
> include/linux/types.h:
> typedef struct {
>     volatile int counter;
> } atomic_t;
> -mike

It's only accessed under a spinlock, so I don't think it needs to be
volatile.  On UP it's accessed within local_irq_save/restore which
should also be compiler barriers and prevent memory access reordering,
so again volatile isn't needed.

Paul.
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