linux-kernel - Re: [PATCH v2 7/7] ARM: atomics: define our SMP atomics in terms of

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Date:	Thu, 16 Jul 2015 20:00:34 -0400
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Will Deacon <will.deacon@....com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v2 7/7] ARM: atomics: define our SMP atomics in terms
 of _relaxed operations

On 07/16/2015 05:08 PM, Peter Zijlstra wrote:
> On Thu, Jul 16, 2015 at 04:40:03PM -0400, Waiman Long wrote:
>> On 07/16/2015 11:32 AM, Will Deacon wrote:
>>> @@ -117,6 +115,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
>>>   #error "SMP is not supported on this platform"
>               ^^^^^^^^^^^^^

That #error is only for ARMv5 or below.

>>>   #endif
>>>
>>> +#define xchg xchg_relaxed
>> Is that a typo? I think xchg() needs to be a full memory barrier.
> Pointless on UP.

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