linux-kernel - Re: Linux 3.19-rc3

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Message-ID: <54BE6020.5060609@hurleysoftware.com>
Date:	Tue, 20 Jan 2015 09:03:12 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kmo@...erainc.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Chris Mason <clm@...com>
Subject: Re: Linux 3.19-rc3

On 01/19/2015 07:30 PM, Paul E. McKenney wrote:
> On Tue, Jan 06, 2015 at 12:47:53PM -0800, Paul E. McKenney wrote:
>> On Tue, Jan 06, 2015 at 02:57:37PM -0500, Peter Hurley wrote:
> 
> [ . . . ]
> 
>> David Miller's call, actually.
>>
>> But the rule is that if it is an atomic read-modify-write operation and it
>> returns a value, then the operation itself needs to include full memory
>> barriers before and after (as in the caller doesn't need to add them).
>> Otherwise, the operation does not need to include memory ordering.
>> Since xchg(), atomic_xchg(), and atomic_long_xchg() all return a value,
>> their implementations must include full memory barriers before and after.
>>
>> Pretty straightforward.  ;-)
> 
> Hello again, Peter,
> 
> Were you going to push a patch clarifying this?

Hi Paul,

As you pointed out, atomic_ops.txt is for arch implementors, so I wasn't
planning on patching that file.

I've been meaning to write up something specifically for everyone else but
my own bugs have kept me from that. [That, and I'm not sure what I write
will be suitable for Documentation.]

Regards,
Peter Hurley
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