On Fri, Jun 28, 2013 at 5:03 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> Steinar reported reallocations of skb->head with IPv6, leading to
> a warning in skb_try_coalesce()
>
> It turns out iwl3945 has several problems :
>
> 1) skb->truesize is underestimated.
> We really consume PAGE_SIZE bytes for a fragment,
> not the frame length.
> 2) 128 bytes of initial headroom is a bit low and forces reallocations.
> 3) We can avoid consuming a full page for small enough frames.
>
> Reported-by: Steinar H. Gunderson <sesse@xxxxxxxxxx>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> ---
> Note : compiled only, I do not have this hardware.
>
> drivers/net/wireless/iwlegacy/3945.c | 30 +++++++++++++++----------
> 1 file changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/wireless/iwlegacy/3945.c b/drivers/net/wireless/iwlegacy/3945.c
> index c092033..ad7294f 100644
> --- a/drivers/net/wireless/iwlegacy/3945.c
> +++ b/drivers/net/wireless/iwlegacy/3945.c
> @@ -483,14 +483,13 @@ il3945_pass_packet_to_mac80211(struct il_priv *il, struct il_rx_buf *rxb,
> struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)IL_RX_DATA(pkt);
> struct il3945_rx_frame_hdr *rx_hdr = IL_RX_HDR(pkt);
> struct il3945_rx_frame_end *rx_end = IL_RX_END(pkt);
> - u16 len = le16_to_cpu(rx_hdr->len);
> + u32 len = le16_to_cpu(rx_hdr->len);
> struct sk_buff *skb;
> __le16 fc = hdr->frame_control;
> + u32 fraglen = PAGE_SIZE << il->hw_params.rx_page_order;
>
> /* We received data from the HW, so stop the watchdog */
> - if (unlikely
> - (len + IL39_RX_FRAME_SIZE >
> - PAGE_SIZE << il->hw_params.rx_page_order)) {
> + if (unlikely(len + IL39_RX_FRAME_SIZE > fraglen)) {
> D_DROP("Corruption detected!\n");
> return;
> }
> @@ -506,26 +505,33 @@ il3945_pass_packet_to_mac80211(struct il_priv *il, struct il_rx_buf *rxb,
> D_INFO("Woke queues - frame received on passive channel\n");
> }
>
> - skb = dev_alloc_skb(128);
> + skb = dev_alloc_skb(256);
> if (!skb) {
> IL_ERR("dev_alloc_skb failed\n");
> return;
> }
>
> if (!il3945_mod_params.sw_crypto)
> - il_set_decrypted_flag(il, (struct ieee80211_hdr *)rxb_addr(rxb),
> + il_set_decrypted_flag(il, (struct ieee80211_hdr *)pkt,
> le32_to_cpu(rx_end->status), stats);
>
> - skb_add_rx_frag(skb, 0, rxb->page,
> - (void *)rx_hdr->payload - (void *)pkt, len,
> - len);
> -
> + /* If frame is small enough to fit into skb->head, copy it
> + * and do not consume a full page
> + */
> + if (len <= 256) {
Presumably this 256 is related to the "dev_alloc_skb(256)"? It might
be worth making this a constant of some sort so they don't
inadvertently drift apart in the future.
> + skb_copy_to_linear_data(skb, rx_hdr->payload, len);
> + skb->tail += len;
> + } else {
> + skb_add_rx_frag(skb, 0, rxb->page,
> + (void *)rx_hdr->payload - (void *)pkt, len,
> + fraglen);
> + il->alloc_rxb_page--;
> + rxb->page = NULL;
> + }
> il_update_stats(il, false, fc, len);
> memcpy(IEEE80211_SKB_RXCB(skb), stats, sizeof(*stats));
>
> ieee80211_rx(il->hw, skb);
> - il->alloc_rxb_page--;
> - rxb->page = NULL;
> }
>
> #define IL_DELAY_NEXT_SCAN_AFTER_ASSOC (HZ*6)
>
>
> --
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