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Date: Tue, 13 Oct 2015 16:04:27 +0100
From: Will Deacon <will.deacon@arm.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
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        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Waiman Long <waiman.long@hp.com>, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v3 6/6] powerpc: atomic: Implement cmpxchg{,64}_* and
 atomic{,64}_cmpxchg_* variants
Message-ID: <20151013150427.GP21550@arm.com>
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On Tue, Oct 13, 2015 at 10:58:30PM +0800, Boqun Feng wrote:
> On Tue, Oct 13, 2015 at 03:43:33PM +0100, Will Deacon wrote:
> > Putting a barrier in the middle of that critical section is probably a
> > terrible idea, and that's why I thought you were avoiding it (hence my
> 
> The fact is that I haven't thought of that way to implement
> cmpxchg_release before you ask that question ;-) And I'm not going to do
> that for now and probably not in the future.
> 
> > original question). Perhaps just add a comment to that effect, since I
> 
> Are you suggesting if I put a barrier in the middle I'd better to add a
> comment, right? So if I don't do that, it's OK to let this patch as it.

No, I mean put a comment in your file to explain the reason why you
override _relaxed and _acquire, but not _release (because overriding
_release would introduce this weird barrier in the middle of the critical
section, which would likely cause the conditional store to fail).

Will