linux-kernel - Re: [PATCH v2 32/32] virtio_ring: use virt_store

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Message-ID: <20160103110052-mutt-send-email-mst@redhat.com>
Date:	Sun, 3 Jan 2016 11:01:05 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	virtualization@...ts.linux-foundation.org,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
	x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v2 32/32] virtio_ring: use virt_store_mb

On Fri, Jan 01, 2016 at 08:23:46PM +0300, Sergei Shtylyov wrote:
> Hello.
> 
> On 12/31/2015 10:09 PM, Michael S. Tsirkin wrote:
> 
> >We need a full barrier after writing out event index, using
> >virt_store_mb there seems better than open-coding.  As usual, we need a
> >wrapper to account for strong barriers.
> >
> >It's tempting to use this in vhost as well, for that, we'll
> >need a variant of smp_store_mb that works on __user pointers.
> >
> >Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> >---
> >  include/linux/virtio_ring.h  | 12 ++++++++++++
> >  drivers/virtio/virtio_ring.c | 15 +++++++++------
> >  2 files changed, 21 insertions(+), 6 deletions(-)
> >
> >diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> >index f3fa55b..3a74d91 100644
> >--- a/include/linux/virtio_ring.h
> >+++ b/include/linux/virtio_ring.h
> >@@ -45,6 +45,18 @@ static inline void virtio_wmb(bool weak_barriers)
> >  		wmb();
> >  }
> >
> >+static inline void virtio_store_mb(bool weak_barriers,
> >+				   __virtio16 *p, __virtio16 v)
> >+{
> >+	if (weak_barriers)
> >+		virt_store_mb(*p, v);
> >+	else
> >+	{
> 
>    The kernel coding style dictates:
> 
> 	if (weak_barriers) {
> 		virt_store_mb(*p, v);
> 	} else {
> 
> >+		WRITE_ONCE(*p, v);
> >+		mb();
> >+	}
> >+}
> >+
> [...]
> 
> MBR, Sergei

Will fix, thanks!
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