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Date: Thu, 20 Sep 2018 14:29:19 -0700
From: Rajkumar Manoharan <rmanohar@codeaurora.org>
To: =?UTF-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
Cc: linux-wireless@vger.kernel.org,
        make-wifi-fast@lists.bufferbloat.net, Felix Fietkau <nbd@nbd.name>,
        Kan Yan <kyan@google.com>
Subject: Re: [PATCH RFC v4 0/4] Move TXQ scheduling into mac80211
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On 2018-09-16 10:42, Toke Høiland-Jørgensen wrote:
> Another update, addressing most of the concerns raised in the last 
> round:
> 
> - Added schedule_start()/end() functions that adds locking around the
>   whole scheduling operation, which means we can get rid of the 'first'
>   parameter to ieee80211_next_txq().
> 
Toke,

Wouldn't this start()/end() APIs cause deadlock if mac80211 tries to 
acquire
active_txq_lock[ac] again? Or am I missing?

schedule_start()
while (next_txq()) {
   push_txq -> tx_dequeue()
   return_txq()
}
schedule_end()

tx_dequeue()
  ieee80211_free_txskb
   -> ieee80211_report_used_skb
    -> ieee80211_tdls_td_tx_handle
     -> ieee80211_subif_start_xmit
     -> __ieee80211_subif_start_xmit
       -> ieee80211_xmit_fast
         -> ieee80211_queue_skb
          -> schedule_and_wake_txq

-Rajkumar