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@@ -0,0 +1,61 @@
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+From: Johannes Berg <[email protected]>
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+Date: Tue, 23 Mar 2021 21:05:01 +0100
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+Subject: [PATCH] mac80211: fix TXQ AC confusion
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+
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+Normally, TXQs have
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+
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+ txq->tid = tid;
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+ txq->ac = ieee80211_ac_from_tid(tid);
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+
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+However, the special management TXQ actually has
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+
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+ txq->tid = IEEE80211_NUM_TIDS; // 16
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+ txq->ac = IEEE80211_AC_VO;
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+
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+This makes sense, but ieee80211_ac_from_tid(16) is the same
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+as ieee80211_ac_from_tid(0) which is just IEEE80211_AC_BE.
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+
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+Now, normally this is fine. However, if the netdev queues
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+were stopped, then the code in ieee80211_tx_dequeue() will
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+propagate the stop from the interface (vif->txqs_stopped[])
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+if the AC 2 (ieee80211_ac_from_tid(txq->tid)) is marked as
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+stopped. On wake, however, __ieee80211_wake_txqs() will wake
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+the TXQ if AC 0 (txq->ac) is woken up.
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+
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+If a driver stops all queues with ieee80211_stop_tx_queues()
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+and then wakes them again with ieee80211_wake_tx_queues(),
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+the ieee80211_wake_txqs() tasklet will run to resync queue
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+and TXQ state. If all queues were woken, then what'll happen
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+is that _ieee80211_wake_txqs() will run in order of HW queues
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+0-3, typically (and certainly for iwlwifi) corresponding to
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+ACs 0-3, so it'll call __ieee80211_wake_txqs() for each AC in
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+order 0-3.
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+
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+When __ieee80211_wake_txqs() is called for AC 0 (VO) that'll
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+wake up the management TXQ (remember its tid is 16), and the
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+driver's wake_tx_queue() will be called. That tries to get a
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+frame, which will immediately *stop* the TXQ again, because
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+now we check against AC 2, and AC 2 hasn't yet been marked as
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+woken up again in sdata->vif.txqs_stopped[] since we're only
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+in the __ieee80211_wake_txqs() call for AC 0.
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+
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+Thus, the management TXQ will never be started again.
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+
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+Fix this by checking txq->ac directly instead of calculating
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+the AC as ieee80211_ac_from_tid(txq->tid).
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+
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+Fixes: adf8ed01e4fd ("mac80211: add an optional TXQ for other PS-buffered frames")
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+Signed-off-by: Johannes Berg <[email protected]>
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+---
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+
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+--- a/net/mac80211/tx.c
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++++ b/net/mac80211/tx.c
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+@@ -3589,7 +3589,7 @@ begin:
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+ test_bit(IEEE80211_TXQ_STOP_NETIF_TX, &txqi->flags))
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+ goto out;
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+
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+- if (vif->txqs_stopped[ieee80211_ac_from_tid(txq->tid)]) {
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++ if (vif->txqs_stopped[txq->ac]) {
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+ set_bit(IEEE80211_TXQ_STOP_NETIF_TX, &txqi->flags);
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+ goto out;
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+ }
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