netdev - Re: [PATCH net-next 12/12] tools/virtio: fix smp

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Date:   Fri, 26 Jan 2018 15:45:33 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        David Miller <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 12/12] tools/virtio: fix smp_mb on x86

On Fri, Jan 26, 2018 at 11:56:14AM +0800, Jason Wang wrote:
> 
> 
> On 2018年01月26日 07:36, Michael S. Tsirkin wrote:
> > Offset 128 overlaps the last word of the redzone.
> > Use 132 which is always beyond that.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> >   tools/virtio/ringtest/main.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/virtio/ringtest/main.h b/tools/virtio/ringtest/main.h
> > index 593a328..301d59b 100644
> > --- a/tools/virtio/ringtest/main.h
> > +++ b/tools/virtio/ringtest/main.h
> > @@ -111,7 +111,7 @@ static inline void busy_wait(void)
> >   }
> >   #if defined(__x86_64__) || defined(__i386__)
> > -#define smp_mb()     asm volatile("lock; addl $0,-128(%%rsp)" ::: "memory", "cc")
> 
> Just wonder did "rsp" work for __i386__ ?
> 
> Thanks

Oh you are right of course. Probably no one ever run this one on i386 :)
I'll add a patch on top as this is not a new bug.

> > +#define smp_mb()     asm volatile("lock; addl $0,-132(%%rsp)" ::: "memory", "cc")
> >   #else
> >   /*
> >    * Not using __ATOMIC_SEQ_CST since gcc docs say they are only synchronized