Linux Virtualization - Jan 2018 - [PATCH net-next 12/12] tools/virtio: fix smp_mb on x86

Offset 128 overlaps the last word of the redzone.
Use 132 which is always beyond that.

Signed-off-by: Michael S. Tsirkin <mst at redhat.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")
+#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
-- 
MST

On 2018?01?26? 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 at redhat.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
> +#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

On Fri, Jan 26, 2018 at 11:56:14AM +0800, Jason Wang
wrote:
> 
> 
> On 2018?01?26? 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 at redhat.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