Re: [Qemu-devel] [PATCH 2/2] rtl8139: flush queued packets when RxBufPtr is written

[Paolo Bonzini <pbonzini@redhat.com>]

Il 24/05/2013 16:38, Stefan Hajnoczi ha scritto:
> Net queues support efficient "receive disable".  For example, tap's file
> descriptor will not be polled while its peer has receive disabled.  This
> saves CPU cycles for needlessly copying and then dropping packets which
> the peer cannot receive.
> 
> rtl8139 is missing the qemu_flush_queued_packets() call that wakes the
> queue up when receive becomes possible again.
> 
> As a result, the Windows 7 guest driver reaches a state where the
> rtl8139 cannot receive packets.  The driver has actually refilled the
> receive buffer but we never resume reception.
> 
> The bug can be reproduced by running a large FTP 'get' inside a Windows
> 7 guest:
> 
>   $ qemu -netdev tap,id=tap0,...
>          -device rtl8139,netdev=tap0
> 
> The Linux guest driver does not trigger the bug, probably due to a
> different buffer management strategy.
> 
> Reported-by: Oliver Francke <oliver.francke@filoo.de>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/net/rtl8139.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
> index 9369507..7993f9f 100644
> --- a/hw/net/rtl8139.c
> +++ b/hw/net/rtl8139.c
> @@ -2575,6 +2575,9 @@ static void rtl8139_RxBufPtr_write(RTL8139State *s, uint32_t val)
>      /* this value is off by 16 */
>      s->RxBufPtr = MOD2(val + 0x10, s->RxBufferSize);
>  
> +    /* more buffer space may be available so try to receive */
> +    qemu_flush_queued_packets(qemu_get_queue(s->nic));
> +
>      DPRINTF(" CAPR write: rx buffer length %d head 0x%04x read 0x%04x\n",
>          s->RxBufferSize, s->RxBufAddr, s->RxBufPtr);
>  }
> 

Do you have time to update the branch with a "Cc: qemu-stable@nongnu.org"?

Paolo