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Date: Wed, 26 Oct 2016 10:08:31 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Abdelrhman Ahmed <ab@...hmed.com> Cc: davem <davem@...emloft.net>, netdev <netdev@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] net: Reset skb to network header in neigh_hh_output On Wed, 2016-10-26 at 18:53 +0200, Abdelrhman Ahmed wrote: > I think it's at the right place as the current one is a little different from the > commit e1f165032c8bade3a6bdf546f8faf61fda4dd01c. > > In the next lines, skb_push is called after copying the hardware header and there > is no change to the data pointer inside the retry loop. We only need to reset > before this loop. > > __skb_pull(skb, skb_network_offset(skb)); > > do { > seq = read_seqbegin(&hh->hh_lock); > hh_len = hh->hh_len; > if (likely(hh_len <= HH_DATA_MOD)) { > /* this is inlined by gcc */ > memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD); > } else { > int hh_alen = HH_DATA_ALIGN(hh_len); > > memcpy(skb->data - hh_alen, hh->hh_data, hh_alen); > } > } while (read_seqretry(&hh->hh_lock, seq)); > > skb_push(skb, hh_len); > > In the commit e1f165032c8bade3a6bdf546f8faf61fda4dd01c, dev_hard_header which > calls create method for adding hardware header (uses skb_push) so it was > required to reset to network header in the beginning of the retry loop. Right you are, thanks for the clarification ! Back to the cause of the bug then. If netfilter is the only case this might be needed, can't this be fixed in netfilter ? neigh_hh_output() is in fast path, it is quite annoying adding this operation.
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