linux-kernel - Re: [PATCH 0/3] virtio/vringh: kill off ACCESS

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Date:   Fri, 25 Nov 2016 22:56:29 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        linux-kernel@...r.kernel.org, dave@...olabs.net, dbueso@...e.de,
        dvyukov@...gle.com, jasowang@...hat.com, kvm@...r.kernel.org,
        netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
        virtualization@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE()

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);					\
> > })