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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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?

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,
-- 
1.7.2.5




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