iwl3945: better skb management in rx path

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@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paul Stewart <pstew@google.com>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/drivers/net/wireless/iwlegacy/3945.c b/drivers/net/wireless/iwlegacy/3945.c
index c092033..f09e257 100644 (file)
--- a/drivers/net/wireless/iwlegacy/3945.c
+++ b/drivers/net/wireless/iwlegacy/3945.c
@@ -475,6 +475,8 @@ il3945_is_network_packet(struct il_priv *il, struct ieee80211_hdr *header)
        }
 }
 
+#define SMALL_PACKET_SIZE 256
+
 static void
 il3945_pass_packet_to_mac80211(struct il_priv *il, struct il_rx_buf *rxb,
                               struct ieee80211_rx_status *stats)
@@ -483,14 +485,13 @@ 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 +507,32 @@ 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(SMALL_PACKET_SIZE);
        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 <= SMALL_PACKET_SIZE) {
+               memcpy(skb_put(skb, len), rx_hdr->payload, 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)