netdev - Re: [PATCH] usbnet: fix oops in usbnet_start

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Date:	Mon, 7 Nov 2011 14:33:51 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Oliver Neukum <oneukum@...e.de>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>, devel@...nvz.org,
	Michael Riesch <michael@...sch.at>
Subject: Re: [PATCH] usbnet: fix oops in usbnet_start_xmit

On Sun, Nov 06, 2011 at 10:33:37PM +0300, Konstantin Khlebnikov wrote:
> This patch fixes the bug added in commit v3.1-rc7-1055-gf9b491e
> SKB can be NULL at this point, at least for cdc-ncm.

What? You mean .ndo_start_xmit is called with skb NULL?

> Let's call skb_tx_timestamp() after driver specific tx-fixup hacks.

No, that won't work.

That call is before the fixup on purpose, because some fixups add
padding in front of the Ethernet payload, and this will spoil the PTP
packet detection filter.

I don't know why the skb can be NULL here. If that is really the case,
then the correct fix is:

	if (skb)
		skb_tx_timestamp(skb);

Thanks,
Richard


> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> ---
>  drivers/net/usb/usbnet.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index 7d60821..485be70 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -1057,8 +1057,6 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
>  	unsigned long		flags;
>  	int retval;
>  
> -	skb_tx_timestamp(skb);
> -
>  	// some devices want funky USB-level framing, for
>  	// win32 driver (usually) and/or hardware quirks
>  	if (info->tx_fixup) {
> @@ -1075,6 +1073,8 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
>  	}
>  	length = skb->len;
>  
> +	skb_tx_timestamp(skb);
> +
>  	if (!(urb = usb_alloc_urb (0, GFP_ATOMIC))) {
>  		netif_dbg(dev, tx_err, dev->net, "no urb\n");
>  		goto drop;
> 
> --
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