package/kernel/mac80211/patches/subsys/370-mac80211-fix-TXQ-AC-confusion.patch

   1 From: Johannes Berg <johannes.berg@intel.com>
   2 Date: Tue, 23 Mar 2021 21:05:01 +0100
   3 Subject: [PATCH] mac80211: fix TXQ AC confusion
   4
   5 Normally, TXQs have
   6
   7   txq->tid = tid;
   8   txq->ac = ieee80211_ac_from_tid(tid);
   9
  10 However, the special management TXQ actually has
  11
  12   txq->tid = IEEE80211_NUM_TIDS; // 16
  13   txq->ac = IEEE80211_AC_VO;
  14
  15 This makes sense, but ieee80211_ac_from_tid(16) is the same
  16 as ieee80211_ac_from_tid(0) which is just IEEE80211_AC_BE.
  17
  18 Now, normally this is fine. However, if the netdev queues
  19 were stopped, then the code in ieee80211_tx_dequeue() will
  20 propagate the stop from the interface (vif->txqs_stopped[])
  21 if the AC 2 (ieee80211_ac_from_tid(txq->tid)) is marked as
  22 stopped. On wake, however, __ieee80211_wake_txqs() will wake
  23 the TXQ if AC 0 (txq->ac) is woken up.
  24
  25 If a driver stops all queues with ieee80211_stop_tx_queues()
  26 and then wakes them again with ieee80211_wake_tx_queues(),
  27 the ieee80211_wake_txqs() tasklet will run to resync queue
  28 and TXQ state. If all queues were woken, then what'll happen
  29 is that _ieee80211_wake_txqs() will run in order of HW queues
  30 0-3, typically (and certainly for iwlwifi) corresponding to
  31 ACs 0-3, so it'll call __ieee80211_wake_txqs() for each AC in
  32 order 0-3.
  33
  34 When __ieee80211_wake_txqs() is called for AC 0 (VO) that'll
  35 wake up the management TXQ (remember its tid is 16), and the
  36 driver's wake_tx_queue() will be called. That tries to get a
  37 frame, which will immediately *stop* the TXQ again, because
  38 now we check against AC 2, and AC 2 hasn't yet been marked as
  39 woken up again in sdata->vif.txqs_stopped[] since we're only
  40 in the __ieee80211_wake_txqs() call for AC 0.
  41
  42 Thus, the management TXQ will never be started again.
  43
  44 Fix this by checking txq->ac directly instead of calculating
  45 the AC as ieee80211_ac_from_tid(txq->tid).
  46
  47 Fixes: adf8ed01e4fd ("mac80211: add an optional TXQ for other PS-buffered frames")
  48 Signed-off-by: Johannes Berg <johannes.berg@intel.com>
  49 ---
  50
  51 --- a/net/mac80211/tx.c
  52 +++ b/net/mac80211/tx.c
  53 @@ -3589,7 +3589,7 @@ begin:
  54             test_bit(IEEE80211_TXQ_STOP_NETIF_TX, &txqi->flags))
  55                 goto out;
  56
  57 -       if (vif->txqs_stopped[ieee80211_ac_from_tid(txq->tid)]) {
  58 +       if (vif->txqs_stopped[txq->ac]) {
  59                 set_bit(IEEE80211_TXQ_STOP_NETIF_TX, &txqi->flags);
  60                 goto out;
  61         }