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Date: Fri, 25 Nov 2016 22:56:29 +0800
From: Boqun Feng <boqun.feng@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org,
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        paulmck@linux.vnet.ibm.com, virtualization@lists.linux-foundation.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE()
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On Fri, Nov 25, 2016 at 01:44:04PM +0100, Peter Zijlstra wrote:
> On Fri, Nov 25, 2016 at 01:40:44PM +0100, Peter Zijlstra wrote:
> > #define SINGLE_LOAD(x)						\
> > {(								\
> > 	compiletime_assert_atomic_type(typeof(x));		\
> 
> Should be:
> 
> 	compiletime_assert_atomic_type(x);
> 
> > 	WARN_SINGLE_COPY_ALIGNMENT(&(x));			\

Do we need to worry about the side effect on x? Maybe

#define SINGLE_LOAD(x)					\
({							\
	typeof(x) *_____ptr;				\
							\
	compiletime_assert_atomic_type(typeof(x));	\
							\
	_____ptr = &(x);				\
							\
	WARN_SINGLE_COPY_ALIGNMENT(_____ptr);		\
							\
	READ_ONCE(*_____ptr);				\
})

Ditto for SINGLE_STORE()

Regards,
Boqun

> > 	READ_ONCE(x);						\
> > })
> > 
> > #define SINGLE_STORE(x, v)					\
> > ({								\
> > 	compiletime_assert_atomic_type(typeof(x));		\
> 
> idem
> 
> > 	WARN_SINGLE_COPY_ALIGNMENT(&(x));			\
> > 	WRITE_ONCE(x, v);					\
> > })