mac80211: fix spurious disconnect issues with disassoc_low_ack=1 (default)

mac80211 reports a packet loss event to user space when 50 consecutive packets
were not acked. On a high throughput link with long aggregates and sudden
link changes, this can trigger way too easily.
Mitigate false positives by only triggering the event on a packet loss if
no ACK was received for at least a second

Signed-off-by: Felix Fietkau <nbd@nbd.name>

diff --git a/package/kernel/mac80211/patches/subsys/310-mac80211-reduce-packet-loss-event-false-positives.patch b/package/kernel/mac80211/patches/subsys/310-mac80211-reduce-packet-loss-event-false-positives.patch
new file mode 100644 (file)
index 0000000..8509438
--- /dev/null
+++ b/package/kernel/mac80211/patches/subsys/310-mac80211-reduce-packet-loss-event-false-positives.patch
@@ -0,0 +1,116 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Sat, 8 Aug 2020 19:20:02 +0200
+Subject: [PATCH] mac80211: reduce packet loss event false positives
+
+When running a large number of packets per second with a high data rate
+and long A-MPDUs, the packet loss threshold can be reached very quickly
+when the link conditions change. This frequently shows up as spurious
+disconnects.
+Mitigate false positives by using a similar logic for regular stations
+as the one being used for TDLS, though with a more aggressive timeout.
+Packet loss events are only reported if no ACK was received for a second.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/sta_info.h
++++ b/net/mac80211/sta_info.h
+@@ -522,7 +522,7 @@ struct ieee80211_sta_rx_stats {
+  * @status_stats.retry_failed: # of frames that failed after retry
+  * @status_stats.retry_count: # of retries attempted
+  * @status_stats.lost_packets: # of lost packets
+- * @status_stats.last_tdls_pkt_time: timestamp of last TDLS packet
++ * @status_stats.last_pkt_time: timestamp of last ACKed packet
+  * @status_stats.msdu_retries: # of MSDU retries
+  * @status_stats.msdu_failed: # of failed MSDUs
+  * @status_stats.last_ack: last ack timestamp (jiffies)
+@@ -595,7 +595,7 @@ struct sta_info {
+               unsigned long filtered;
+               unsigned long retry_failed, retry_count;
+               unsigned int lost_packets;
+-              unsigned long last_tdls_pkt_time;
++              unsigned long last_pkt_time;
+               u64 msdu_retries[IEEE80211_NUM_TIDS + 1];
+               u64 msdu_failed[IEEE80211_NUM_TIDS + 1];
+               unsigned long last_ack;
+--- a/net/mac80211/status.c
++++ b/net/mac80211/status.c
+@@ -749,12 +749,16 @@ static void ieee80211_report_used_skb(st
+  *  - current throughput (higher value for higher tpt)?
+  */
+ #define STA_LOST_PKT_THRESHOLD        50
++#define STA_LOST_PKT_TIME     HZ              /* 1 sec since last ACK */
+ #define STA_LOST_TDLS_PKT_THRESHOLD   10
+ #define STA_LOST_TDLS_PKT_TIME                (10*HZ) /* 10secs since last ACK */
+ 
+ static void ieee80211_lost_packet(struct sta_info *sta,
+                                 struct ieee80211_tx_info *info)
+ {
++      unsigned long pkt_time = STA_LOST_PKT_TIME;
++      unsigned int pkt_thr = STA_LOST_PKT_THRESHOLD;
++
+       /* If driver relies on its own algorithm for station kickout, skip
+        * mac80211 packet loss mechanism.
+        */
+@@ -767,21 +771,20 @@ static void ieee80211_lost_packet(struct
+               return;
+ 
+       sta->status_stats.lost_packets++;
+-      if (!sta->sta.tdls &&
+-          sta->status_stats.lost_packets < STA_LOST_PKT_THRESHOLD)
+-              return;
++      if (sta->sta.tdls) {
++              pkt_time = STA_LOST_TDLS_PKT_TIME;
++              pkt_thr = STA_LOST_PKT_THRESHOLD;
++      }
+ 
+       /*
+        * If we're in TDLS mode, make sure that all STA_LOST_TDLS_PKT_THRESHOLD
+        * of the last packets were lost, and that no ACK was received in the
+        * last STA_LOST_TDLS_PKT_TIME ms, before triggering the CQM packet-loss
+        * mechanism.
++       * For non-TDLS, use STA_LOST_PKT_THRESHOLD and STA_LOST_PKT_TIME
+        */
+-      if (sta->sta.tdls &&
+-          (sta->status_stats.lost_packets < STA_LOST_TDLS_PKT_THRESHOLD ||
+-           time_before(jiffies,
+-                       sta->status_stats.last_tdls_pkt_time +
+-                       STA_LOST_TDLS_PKT_TIME)))
++      if (sta->status_stats.lost_packets < pkt_thr ||
++          !time_after(jiffies, sta->status_stats.last_pkt_time + pkt_time))
+               return;
+ 
+       cfg80211_cqm_pktloss_notify(sta->sdata->dev, sta->sta.addr,
+@@ -1034,9 +1037,7 @@ static void __ieee80211_tx_status(struct
+                                       sta->status_stats.lost_packets = 0;
+ 
+                               /* Track when last TDLS packet was ACKed */
+-                              if (test_sta_flag(sta, WLAN_STA_TDLS_PEER_AUTH))
+-                                      sta->status_stats.last_tdls_pkt_time =
+-                                              jiffies;
++                              sta->status_stats.last_pkt_time = jiffies;
+                       } else if (noack_success) {
+                               /* nothing to do here, do not account as lost */
+                       } else {
+@@ -1169,9 +1170,8 @@ void ieee80211_tx_status_ext(struct ieee
+                       if (sta->status_stats.lost_packets)
+                               sta->status_stats.lost_packets = 0;
+ 
+-                      /* Track when last TDLS packet was ACKed */
+-                      if (test_sta_flag(sta, WLAN_STA_TDLS_PEER_AUTH))
+-                              sta->status_stats.last_tdls_pkt_time = jiffies;
++                      /* Track when last packet was ACKed */
++                      sta->status_stats.last_pkt_time = jiffies;
+               } else if (test_sta_flag(sta, WLAN_STA_PS_STA)) {
+                       return;
+               } else if (noack_success) {
+@@ -1260,8 +1260,7 @@ void ieee80211_tx_status_8023(struct iee
+                       if (sta->status_stats.lost_packets)
+                               sta->status_stats.lost_packets = 0;
+ 
+-                      if (test_sta_flag(sta, WLAN_STA_TDLS_PEER_AUTH))
+-                              sta->status_stats.last_tdls_pkt_time = jiffies;
++                      sta->status_stats.last_pkt_time = jiffies;
+               } else {
+                       ieee80211_lost_packet(sta, info);
+               }