Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum_dev
From: Jarek Poplawski <hidden>
Date: 2010-09-04 20:34:39
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lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Eric Dumazet wrote, On 09/01/2010 12:50 PM:
quoted hunk ↗ jump to hunk
[PATCH] gro: fix different skb headrooms packets entering GRO might have different headrooms, even for a given flow (because of implementation details in drivers, like copybreak). We cant force drivers to deliver packets with a fixed headroom. 1) fix skb_segment() skb_segment() makes the false assumption headrooms of fragments are same than the head. When CHECKSUM_PARTIAL is used, this can give csum_start errors, and crash later in skb_copy_and_csum_dev() 2) allocate a minimal skb for head of frag_list skb_gro_receive() uses netdev_alloc_skb(headroom + skb_gro_offset(p)) to allocate a fresh skb. This adds NET_SKB_PAD to a padding already provided by netdevice, depending on various things, like copybreak. Use alloc_skb() to allocate an exact padding, to reduce cache line needs: NET_SKB_PAD + NET_IP_ALIGN bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=16626 Many thanks to Plamen Petrov, testing many debugging patches ! With help of Jarek Poplawski. Reported-by: Plamen Petrov <redacted> Signed-off-by: Eric Dumazet <redacted> CC: Jarek Poplawski <redacted> --- patch against linux-2.6 current tree net/core/skbuff.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)diff --git a/net/core/skbuff.c b/net/core/skbuff.c
...
quoted hunk ↗ jump to hunk
@@ -2702,8 +2706,8 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb) } else if (skb_gro_len(p) != pinfo->gso_size) return -E2BIG; - headroom = skb_headroom(p); - nskb = netdev_alloc_skb(p->dev, headroom + skb_gro_offset(p)); + headroom = NET_SKB_PAD + NET_IP_ALIGN; + nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC); if (unlikely(!nskb)) return -ENOMEM;
Hi again, Just had a second look, and unless I miss something... Plamen, could you test this patch, too? (Without removing the previous one.) Thanks, Jarek P. -------------------> [PATCH] gro: Re-fix different skb headrooms The patch: "gro: fix different skb headrooms" in its part: "2) allocate a minimal skb for head of frag_list" is buggy. The copied skb has p->data set at the ip header at the moment, and skb_gro_offset is the length of ip + tcp headers. So, after the change the length of mac header is skipped. Later skb_set_mac_header() sets it into the NET_SKB_PAD area (if it's long enough) and ip header is misaligned at NET_SKB_PAD + NET_IP_ALIGN offset. There is no reason to assume the original skb was wrongly allocated, so let's copy it as it was. bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=16626 fixes commit: 3d3be4333fdf6faa080947b331a6a19bce1a4f57 Reported-by: Plamen Petrov <redacted> Signed-off-by: Jarek Poplawski <redacted> CC: Eric Dumazet <redacted> ---
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 26396ff..c83b421 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c@@ -2706,7 +2706,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb) } else if (skb_gro_len(p) != pinfo->gso_size) return -E2BIG; - headroom = NET_SKB_PAD + NET_IP_ALIGN; + headroom = skb_headroom(p); nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC); if (unlikely(!nskb)) return -ENOMEM;