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

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Date:	Thu, 18 Jun 2009 20:49:02 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Paul Mackerras <paulus@...ba.org>
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

On Thu, Jun 18, 2009 at 20:47, Paul Mackerras wrote:
> 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;
>
> 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.

i'm not suggesting it is needed, i'm saying it's a bit confusing.  a
simple comment above the atomic64_t type with your simple explanation
here would go a long way.
-mike
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