mac80211: rework TX filtered frame code
This reworks the code for TX filtered frames, splitting it out to
a new function to handle those cases, making the clear instruction
a flag and renaming a few things to be easier to understand and
less Atheros hardware specific. Finally, it also makes the comments
explain more.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/ieee80211.c b/net/mac80211/ieee80211.c
index 7df1479..a00858d 100644
--- a/net/mac80211/ieee80211.c
+++ b/net/mac80211/ieee80211.c
@@ -1178,6 +1178,77 @@
}
}
+static void ieee80211_handle_filtered_frame(struct ieee80211_local *local,
+ struct sta_info *sta,
+ struct sk_buff *skb,
+ struct ieee80211_tx_status *status)
+{
+ sta->tx_filtered_count++;
+
+ /*
+ * Clear the TX filter mask for this STA when sending the next
+ * packet. If the STA went to power save mode, this will happen
+ * happen when it wakes up for the next time.
+ */
+ sta->flags |= WLAN_STA_CLEAR_PS_FILT;
+
+ /*
+ * This code races in the following way:
+ *
+ * (1) STA sends frame indicating it will go to sleep and does so
+ * (2) hardware/firmware adds STA to filter list, passes frame up
+ * (3) hardware/firmware processes TX fifo and suppresses a frame
+ * (4) we get TX status before having processed the frame and
+ * knowing that the STA has gone to sleep.
+ *
+ * This is actually quite unlikely even when both those events are
+ * processed from interrupts coming in quickly after one another or
+ * even at the same time because we queue both TX status events and
+ * RX frames to be processed by a tasklet and process them in the
+ * same order that they were received or TX status last. Hence, there
+ * is no race as long as the frame RX is processed before the next TX
+ * status, which drivers can ensure, see below.
+ *
+ * Note that this can only happen if the hardware or firmware can
+ * actually add STAs to the filter list, if this is done by the
+ * driver in response to set_tim() (which will only reduce the race
+ * this whole filtering tries to solve, not completely solve it)
+ * this situation cannot happen.
+ *
+ * To completely solve this race drivers need to make sure that they
+ * (a) don't mix the irq-safe/not irq-safe TX status/RX processing
+ * functions and
+ * (b) always process RX events before TX status events if ordering
+ * can be unknown, for example with different interrupt status
+ * bits.
+ */
+ if (sta->flags & WLAN_STA_PS &&
+ skb_queue_len(&sta->tx_filtered) < STA_MAX_TX_BUFFER) {
+ ieee80211_remove_tx_extra(local, sta->key, skb,
+ &status->control);
+ skb_queue_tail(&sta->tx_filtered, skb);
+ return;
+ }
+
+ if (!(sta->flags & WLAN_STA_PS) &&
+ !(status->control.flags & IEEE80211_TXCTL_REQUEUE)) {
+ /* Software retry the packet once */
+ status->control.flags |= IEEE80211_TXCTL_REQUEUE;
+ ieee80211_remove_tx_extra(local, sta->key, skb,
+ &status->control);
+ dev_queue_xmit(skb);
+ return;
+ }
+
+ if (net_ratelimit())
+ printk(KERN_DEBUG "%s: dropped TX filtered frame, "
+ "queue_len=%d PS=%d @%lu\n",
+ wiphy_name(local->hw.wiphy),
+ skb_queue_len(&sta->tx_filtered),
+ !!(sta->flags & WLAN_STA_PS), jiffies);
+ dev_kfree_skb(skb);
+}
+
void ieee80211_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
struct ieee80211_tx_status *status)
{
@@ -1202,11 +1273,16 @@
sta = sta_info_get(local, hdr->addr1);
if (sta) {
if (sta->flags & WLAN_STA_PS) {
- /* The STA is in power save mode, so assume
+ /*
+ * The STA is in power save mode, so assume
* that this TX packet failed because of that.
*/
status->excessive_retries = 0;
status->flags |= IEEE80211_TX_STATUS_TX_FILTERED;
+ ieee80211_handle_filtered_frame(local, sta,
+ skb, status);
+ sta_info_put(sta);
+ return;
}
sta_info_put(sta);
}
@@ -1216,47 +1292,8 @@
struct sta_info *sta;
sta = sta_info_get(local, hdr->addr1);
if (sta) {
- sta->tx_filtered_count++;
-
- /* Clear the TX filter mask for this STA when sending
- * the next packet. If the STA went to power save mode,
- * this will happen when it is waking up for the next
- * time. */
- sta->clear_dst_mask = 1;
-
- /* TODO: Is the WLAN_STA_PS flag always set here or is
- * the race between RX and TX status causing some
- * packets to be filtered out before 80211.o gets an
- * update for PS status? This seems to be the case, so
- * no changes are likely to be needed. */
- if (sta->flags & WLAN_STA_PS &&
- skb_queue_len(&sta->tx_filtered) <
- STA_MAX_TX_BUFFER) {
- ieee80211_remove_tx_extra(local, sta->key,
- skb,
- &status->control);
- skb_queue_tail(&sta->tx_filtered, skb);
- } else if (!(sta->flags & WLAN_STA_PS) &&
- !(status->control.flags & IEEE80211_TXCTL_REQUEUE)) {
- /* Software retry the packet once */
- status->control.flags |= IEEE80211_TXCTL_REQUEUE;
- ieee80211_remove_tx_extra(local, sta->key,
- skb,
- &status->control);
- dev_queue_xmit(skb);
- } else {
- if (net_ratelimit()) {
- printk(KERN_DEBUG "%s: dropped TX "
- "filtered frame queue_len=%d "
- "PS=%d @%lu\n",
- wiphy_name(local->hw.wiphy),
- skb_queue_len(
- &sta->tx_filtered),
- !!(sta->flags & WLAN_STA_PS),
- jiffies);
- }
- dev_kfree_skb(skb);
- }
+ ieee80211_handle_filtered_frame(local, sta, skb,
+ status);
sta_info_put(sta);
return;
}