Linux Virtualization - Jan 2014 - [PATCH stable-only] virtio-net: fix build on m68k and sparc64

As a result of backporting a bugfix, virtio_net started passing void *
to page_address, assuming that it will get silently converted to struct
page *. But this does not happen on architectures where page_address is
a macro, the result is build failure as the macro tries to dereference
void*.

Fix by reordering code slightly, so we always pass
struct page * to page_address.

Reported-by: Guenter Roeck <linux at roeck-us.net>
Tested-by: Guenter Roeck <linux at roeck-us.net>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: David Miller <davem at davemloft.net>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---

David, Greg asked that this be put in stable ASAP to avoid
next release being broken.
I still didn't Cc stable directly as I know you prefer to do this
yourself.
Sorry about creating this mess, could you help fast-path it there please?

Thanks!

 drivers/net/virtio_net.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index b8665588..c8d5ee1 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -330,9 +330,9 @@ static struct sk_buff *receive_mergeable(struct net_device
*dev,
 					 void *buf,
 					 unsigned int len)
 {
-	struct skb_vnet_hdr *hdr = page_address(buf);
-	int num_buf = hdr->mhdr.num_buffers;
 	struct page *page = buf;
+	struct skb_vnet_hdr *hdr = page_address(page);
+	int num_buf = hdr->mhdr.num_buffers;
 	struct sk_buff *skb = page_to_skb(rq, page, len);
 	int i;
 
-- 
MST

On Wed, Jan 15, 2014 at 9:26 AM, Michael S. Tsirkin <mst at redhat.com>
wrote:
> As a result of backporting a bugfix, virtio_net started passing void *
> to page_address, assuming that it will get silently converted to struct
> page *. But this does not happen on architectures where page_address is
> a macro, the result is build failure as the macro tries to dereference
> void*.
>
> Fix by reordering code slightly, so we always pass
> struct page * to page_address.
Thanks for the clue! I was just investigating a similar failure in -next.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at
linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or
something like that.
                                -- Linus Torvalds

On Wed, Jan 15, 2014 at 09:36:13AM +0100, Geert Uytterhoeven
wrote:
> On Wed, Jan 15, 2014 at 9:26 AM, Michael S. Tsirkin <mst at
redhat.com> wrote:
> > As a result of backporting a bugfix, virtio_net started passing void *
> > to page_address, assuming that it will get silently converted to
struct
> > page *. But this does not happen on architectures where page_address
is
> > a macro, the result is build failure as the macro tries to dereference
> > void*.
> >
> > Fix by reordering code slightly, so we always pass
> > struct page * to page_address.
> 
> Thanks for the clue! I was just investigating a similar failure in -next.
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
You don't mean linux-next? And not in virtio-net? I don't see
page_address
being used on void * anywhere there.
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at
linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker.
But
> when I'm talking to journalists I just say "programmer" or
something like that.
>                                 -- Linus Torvalds