Re: [Xen-devel] [Linux 3.7-rc8] DomU: WARNING: at net/core/skbuff.c:3444 skb_try_coalesce+0x359/0x390()

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Monday, December 10, 2012, 4:12:18 PM, you wrote:

> I wrote
>> > I have a vague recollection of a patch to set skb->truesize more
>> > accurately in xennet_poll (netfront), but I can't seem to find any
>> > reference to it now.

> I finally found the following in my git tree. Looks like I never sent it
> out.

> Does it help?

I will give it a try, but i have no easy mean of triggering it, so it could 
take some time to have some certainty.

Thx !

Sander

> 8<--------------------

> From 788ba317fa241512be7a8630b1b58e53faff83ed Mon Sep 17 00:00:00 2001
> From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Date: Wed, 22 Aug 2012 11:55:31 +0100
> Subject: [PATCH] xen/netfront: improve truesize tracking

> Fixes WARN_ON from skb_try_coalesce.

> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
>  drivers/net/xen-netfront.c |   15 +++++----------
>  net/core/skbuff.c          |    2 +-
>  2 files changed, 6 insertions(+), 11 deletions(-)

> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index caa0110..b06ef81 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -971,17 +971,12 @@ err:
>                  * overheads. Here, we add the size of the data pulled
>                  * in xennet_fill_frags().
>                  *
> -                * We also adjust for any unused space in the main
> -                * data area by subtracting (RX_COPY_THRESHOLD -
> -                * len). This is especially important with drivers
> -                * which split incoming packets into header and data,
> -                * using only 66 bytes of the main data area (see the
> -                * e1000 driver for example.)  On such systems,
> -                * without this last adjustement, our achievable
> -                * receive throughout using the standard receive
> -                * buffer size was cut by 25%(!!!).
> +                * We also adjust for the __pskb_pull_tail done in
> +                * handle_incoming_queue which pulls data from the
> +                * frags into the head area, which is already
> +                * accounted in RX_COPY_THRESHOLD.
>                  */
> -               skb->truesize += skb->data_len - RX_COPY_THRESHOLD;
> +               skb->truesize += skb->data_len - 
> NETFRONT_SKB_CB(skb)->pull_to;
>                 skb->len += skb->data_len;
>  
>                 if (rx->flags & XEN_NETRXF_csum_blank)
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 6e04b1f..941a974 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3439,7 +3439,7 @@ bool skb_try_coalesce(struct sk_buff *to, struct 
> sk_buff *from,
>                 delta = from->truesize - SKB_TRUESIZE(skb_end_offset(from));
>         }
>  
> -       WARN_ON_ONCE(delta < len);
> +       WARN_ONCE(delta < len, "delta %d < len %d\n", delta, len);
>  
>         memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
>                skb_shinfo(from)->frags,


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