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

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Message-ID: <55A93896.3090905@hp.com>
Date:	Fri, 17 Jul 2015 13:17:10 -0400
From:	Waiman Long <waiman.long@...com>
To:	Will Deacon <will.deacon@....com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 7/7] ARM: atomics: define our SMP atomics in terms
 of _relaxed operations

On 07/17/2015 05:35 AM, Will Deacon wrote:
> On Fri, Jul 17, 2015 at 01:00:34AM +0100, Waiman Long wrote:
>> 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.
> I don't see the problem here. As Peter pointed out, this code only gets
> looked at if !SMP and structuring it this way means I can have one
> definition of xchg_relaxed, regardless of architecture version.
>
> Will

I am sorry that I got confused as to where it is defined. It should be 
OK in this case.

Cheers,
Longman
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