On Wed, Apr 22, 2015 at 1:21 PM, Alexander Duyck <alexander.du...@gmail.com> wrote: > On 04/22/2015 01:14 PM, Cong Wang wrote: >> On Wed, Apr 22, 2015 at 12:43 PM, Alexander Duyck >> <alexander.du...@gmail.com> wrote: >>> On 04/22/2015 10:45 AM, Cong Wang wrote: >>>> The second parameter of eth_get_headlen() is the length of >>>> the frame buffer, not the header length of skb. >>>> >>>> Cc: Jeff Kirsher <jeffrey.t.kirs...@intel.com> >>>> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com> >>>> --- >>>> drivers/net/ethernet/intel/igb/igb_main.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c >>>> b/drivers/net/ethernet/intel/igb/igb_main.c >>>> index a0a9b1f..7b3a370 100644 >>>> --- a/drivers/net/ethernet/intel/igb/igb_main.c >>>> +++ b/drivers/net/ethernet/intel/igb/igb_main.c >>>> @@ -6852,7 +6852,9 @@ static void igb_pull_tail(struct igb_ring *rx_ring, >>>> /* we need the header to contain the greater of either ETH_HLEN or >>>> * 60 bytes if the skb->len is less than 60 for skb_pad. >>>> */ >>>> - pull_len = eth_get_headlen(va, IGB_RX_HDR_LEN); >>>> + pull_len = eth_get_headlen(va, skb_frag_size(frag)); >>>> + if (unlikely(pull_len > IGB_RX_HDR_LEN)) >>>> + pull_len = IGB_RX_HDR_LEN; >>>> >>>> /* align pull length to size of long to optimize memcpy performance >>>> */ >>>> skb_copy_to_linear_data(skb, va, ALIGN(pull_len, sizeof(long))); >>> You have this part right. The length represents the maximum length we >>> are willing to traverse in the buffer. So if we 100% want to get the >>> entire header regardless of what we can copy into then we could follow >>> your approach. However, since the allocated space in the skb is only >>> IGB_RX_HDR_LEN we only really want to traverse up to that length. Then >>> that is all we copy out of the header. >> But the frag size could be smaller than IGB_RX_HDR_LEN which is >> the case this patch tries to fix. > > No it can't. We only add frags if the first frag is larger than > IGB_RX_HDR_LEN. Go look at the code where this driver calls > add_rx_frag. You should find there is copybreak code in there that > kicks in for anything less than or equal to IGB_RX_HDR_LEN in size on > the first frag. It is there to allow us to avoid having to perform an > atomic inc/dec on the page. >
First, make sure you don't miss the TSIP case right above: The frag starting pointer and its size are advanced by: skb_frag_size_sub(frag, IGB_TS_HDR_LEN); ... va += IGB_TS_HDR_LEN; even though we unlikely pull header longer than IGB_RX_HDR_LEN - IGB_TS_HDR_LEN either. Second, the check you mentioned above is: if ((size <= IGB_RX_HDR_LEN) && !skb_is_nonlinear(skb)) skb is nonlinear _after_ the first igb_add_rx_frag(), a second igb_add_rx_frag() is possible since igb_is_non_eop() could return true. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
