Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:
> On 2019-09-18 05:10, Toke Høiland-Jørgensen wrote:
>> Yibo Zhao <yiboz@xxxxxxxxxxxxxx> writes:
>>
>>> In a loop txqs dequeue scenario, if the first txq in the rbtree gets
>>> removed from rbtree immediately in the ieee80211_return_txq(), the
>>> loop will break soon in the ieee80211_next_txq() due to schedule_pos
>>> not leading to the second txq in the rbtree. Thus, defering the
>>> removal right before the end of this schedule round.
>>>
>>> Co-developed-by: Yibo Zhao <yiboz@xxxxxxxxxxxxxx>
>>> Signed-off-by: Yibo Zhao <yiboz@xxxxxxxxxxxxxx>
>>> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxx>
>>
>> I didn't write this patch, so please don't use my sign-off. I'll add
>> ack or review tags as appropriate in reply; but a few comments first:
>>
>>> ---
>>> include/net/mac80211.h | 16 ++++++++++--
>>> net/mac80211/ieee80211_i.h | 3 +++
>>> net/mac80211/main.c | 6 +++++
>>> net/mac80211/tx.c | 63
>>> +++++++++++++++++++++++++++++++++++++++++++---
>>> 4 files changed, 83 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
>>> index ac2ed8e..ba5a345 100644
>>> --- a/include/net/mac80211.h
>>> +++ b/include/net/mac80211.h
>>> @@ -925,6 +925,8 @@ struct ieee80211_tx_rate {
>>>
>>> #define IEEE80211_MAX_TX_RETRY 31
>>>
>>> +#define IEEE80211_AIRTIME_TXQ_RM_CHK_INTV_IN_MS 100
>>> +
>>> static inline void ieee80211_rate_set_vht(struct ieee80211_tx_rate
>>> *rate,
>>> u8 mcs, u8 nss)
>>> {
>>> @@ -6232,7 +6234,8 @@ struct sk_buff *ieee80211_tx_dequeue(struct
>>> ieee80211_hw *hw,
>>> * @ac: AC number to return packets from.
>>> *
>>> * Should only be called between calls to
>>> ieee80211_txq_schedule_start()
>>> - * and ieee80211_txq_schedule_end().
>>> + * and ieee80211_txq_schedule_end(). If the txq is empty, it will be
>>> added
>>> + * to a remove list and get removed later.
>>> * Returns the next txq if successful, %NULL if no queue is eligible.
>>> If a txq
>>> * is returned, it should be returned with ieee80211_return_txq()
>>> after the
>>> * driver has finished scheduling it.
>>> @@ -6268,7 +6271,8 @@ void ieee80211_txq_schedule_start(struct
>>> ieee80211_hw *hw, u8 ac)
>>> * @hw: pointer as obtained from ieee80211_alloc_hw()
>>> * @ac: AC number to acquire locks for
>>> *
>>> - * Release locks previously acquired by ieee80211_txq_schedule_end().
>>> + * Release locks previously acquired by ieee80211_txq_schedule_end().
>>> Check
>>> + * and remove the empty txq from rb-tree.
>>> */
>>> void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
>>> __releases(txq_lock);
>>> @@ -6287,6 +6291,14 @@ void ieee80211_schedule_txq(struct ieee80211_hw
>>> *hw, struct ieee80211_txq *txq)
>>> __acquires(txq_lock) __releases(txq_lock);
>>>
>>> /**
>>> + * ieee80211_txqs_check - Check txqs waiting for removal
>>> + *
>>> + * @tmr: pointer as obtained from local
>>> + *
>>> + */
>>> +void ieee80211_txqs_check(struct timer_list *tmr);
>>> +
>>> +/**
>>> * ieee80211_txq_may_transmit - check whether TXQ is allowed to
>>> transmit
>>> *
>>> * This function is used to check whether given txq is allowed to
>>> transmit by
>>> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
>>> index a4556f9..49aa143e 100644
>>> --- a/net/mac80211/ieee80211_i.h
>>> +++ b/net/mac80211/ieee80211_i.h
>>> @@ -847,6 +847,7 @@ struct txq_info {
>>> struct codel_stats cstats;
>>> struct sk_buff_head frags;
>>> struct rb_node schedule_order;
>>> + struct list_head candidate;
>>> unsigned long flags;
>>>
>>> /* keep last! */
>>> @@ -1145,6 +1146,8 @@ struct ieee80211_local {
>>> u64 airtime_v_t[IEEE80211_NUM_ACS];
>>> u64 airtime_weight_sum[IEEE80211_NUM_ACS];
>>>
>>> + struct list_head remove_list[IEEE80211_NUM_ACS];
>>> + struct timer_list remove_timer;
>>> u16 airtime_flags;
>>>
>>> const struct ieee80211_ops *ops;
>>> diff --git a/net/mac80211/main.c b/net/mac80211/main.c
>>> index e9ffa8e..78fe24a 100644
>>> --- a/net/mac80211/main.c
>>> +++ b/net/mac80211/main.c
>>> @@ -667,10 +667,15 @@ struct ieee80211_hw
>>> *ieee80211_alloc_hw_nm(size_t priv_data_len,
>>>
>>> for (i = 0; i < IEEE80211_NUM_ACS; i++) {
>>> local->active_txqs[i] = RB_ROOT_CACHED;
>>> + INIT_LIST_HEAD(&local->remove_list[i]);
>>> spin_lock_init(&local->active_txq_lock[i]);
>>> }
>>> local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;
>>>
>>> + timer_setup(&local->remove_timer, ieee80211_txqs_check, 0);
>>> + mod_timer(&local->remove_timer,
>>> + jiffies +
>>> msecs_to_jiffies(IEEE80211_AIRTIME_TXQ_RM_CHK_INTV_IN_MS));
>>> +
>>> INIT_LIST_HEAD(&local->chanctx_list);
>>> mutex_init(&local->chanctx_mtx);
>>>
>>> @@ -1305,6 +1310,7 @@ void ieee80211_unregister_hw(struct ieee80211_hw
>>> *hw)
>>> tasklet_kill(&local->tx_pending_tasklet);
>>> tasklet_kill(&local->tasklet);
>>>
>>> + del_timer_sync(&local->remove_timer);
>>> #ifdef CONFIG_INET
>>> unregister_inetaddr_notifier(&local->ifa_notifier);
>>> #endif
>>> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
>>> index d00baaa..42ca010 100644
>>> --- a/net/mac80211/tx.c
>>> +++ b/net/mac80211/tx.c
>>> @@ -1450,6 +1450,7 @@ void ieee80211_txq_init(struct
>>> ieee80211_sub_if_data *sdata,
>>> codel_stats_init(&txqi->cstats);
>>> __skb_queue_head_init(&txqi->frags);
>>> RB_CLEAR_NODE(&txqi->schedule_order);
>>> + INIT_LIST_HEAD(&txqi->candidate);
>>>
>>> txqi->txq.vif = &sdata->vif;
>>>
>>> @@ -3724,6 +3725,9 @@ void ieee80211_schedule_txq(struct ieee80211_hw
>>> *hw,
>>>
>>> spin_lock_bh(&local->active_txq_lock[ac]);
>>>
>>> + if (!list_empty(&txqi->candidate))
>>> + list_del_init(&txqi->candidate);
>>> +
>>> if (!RB_EMPTY_NODE(&txqi->schedule_order))
>>> goto out;
>>>
>>> @@ -3783,6 +3787,20 @@ static void __ieee80211_unschedule_txq(struct
>>> ieee80211_hw *hw,
>>> RB_CLEAR_NODE(&txqi->schedule_order);
>>> }
>>>
>>> +void ieee80211_remove_txq(struct ieee80211_hw *hw,
>>> + struct ieee80211_txq *txq)
>>> +{
>>> + struct ieee80211_local *local = hw_to_local(hw);
>>> + struct txq_info *txqi = to_txq_info(txq);
>>> +
>>> + lockdep_assert_held(&local->active_txq_lock[txq->ac]);
>>> +
>>> + if (!RB_EMPTY_NODE(&txqi->schedule_order)) {
>>> + __ieee80211_unschedule_txq(hw, txq);
>>> + list_del_init(&txqi->candidate);
>>> + }
>>> +}
>>> +
>>> void ieee80211_unschedule_txq(struct ieee80211_hw *hw,
>>> struct ieee80211_txq *txq)
>>> __acquires(txq_lock) __releases(txq_lock)
>>> @@ -3790,7 +3808,7 @@ void ieee80211_unschedule_txq(struct
>>> ieee80211_hw *hw,
>>> struct ieee80211_local *local = hw_to_local(hw);
>>>
>>> spin_lock_bh(&local->active_txq_lock[txq->ac]);
>>> - __ieee80211_unschedule_txq(hw, txq);
>>> + ieee80211_remove_txq(hw, txq);
>>> spin_unlock_bh(&local->active_txq_lock[txq->ac]);
>>> }
>>>
>>> @@ -3803,11 +3821,48 @@ void ieee80211_return_txq(struct ieee80211_hw
>>> *hw,
>>> lockdep_assert_held(&local->active_txq_lock[txq->ac]);
>>>
>>> if (!RB_EMPTY_NODE(&txqi->schedule_order) &&
>>> - (skb_queue_empty(&txqi->frags) && !txqi->tin.backlog_packets))
>>> - __ieee80211_unschedule_txq(hw, txq);
>>> + !txq_has_queue(&txqi->txq) &&
>>> + list_empty(&txqi->candidate))
>>> + list_add_tail(&txqi->candidate, &local->remove_list[txq->ac]);
>>> +
>>> }
>>> EXPORT_SYMBOL(ieee80211_return_txq);
>>>
>>> +void __ieee80211_check_txqs(struct ieee80211_local *local, int ac)
>>> +{
>>> + struct txq_info *iter, *tmp;
>>> + struct sta_info *sta;
>>> +
>>> + lockdep_assert_held(&local->active_txq_lock[ac]);
>>> +
>>> + list_for_each_entry_safe(iter, tmp, &local->remove_list[ac],
>>> + candidate) {
>>> + sta = container_of(iter->txq.sta, struct sta_info, sta);
>>> +
>>> + if (txq_has_queue(&iter->txq))
>>> + list_del_init(&iter->candidate);
>>> + else
>>> + ieee80211_remove_txq(&local->hw, &iter->txq);
>>> + }
>>> +}
>>> +
>>> +void ieee80211_txqs_check(struct timer_list *t)
>>> +{
>>> + struct ieee80211_local *local = from_timer(local, t, remove_timer);
>>> + struct txq_info *iter, *tmp;
>>> + struct sta_info *sta;
>>> + int ac;
>>> +
>>> + for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
>>> + spin_lock_bh(&local->active_txq_lock[ac]);
>>> + __ieee80211_check_txqs(local, ac);
>>> + spin_unlock_bh(&local->active_txq_lock[ac]);
>>> + }
>>> +
>>> + mod_timer(&local->remove_timer,
>>> + jiffies +
>>> msecs_to_jiffies(IEEE80211_AIRTIME_TXQ_RM_CHK_INTV_IN_MS));
>>> +}
>>
>> I'll ask the same as I did last time (where you told me to hold off
>> until this round):
>>
>> Why do you need the timer and the periodic check? If TXQs are added to
>> the remove list during the scheduling run, and __ieee80211_check_txqs()
>> is run from schedule_end(), isn't that sufficient to clear the list?
> Is it possible that a txq is not added to the remove list but then
> packets in it are dropped by fq_codel algo? Like the station disconnects
> without any notification.
Well as long as all the other cleanup paths call directly into
__unschedule_txq(), that should remove stations from the scheduler when
they disconnect etc.
We only need to defer removal inside a single "scheduling round" (i.e.,
between a pair of ieee80211_txq_schedule_start/end. So if we just walk
the remove list in schedule_end() we should be enough, no?
Hmm, or maybe a simpler way to fix the original issue is just to have
unschedule_txq() update the schedule_pos() pointer?
I.e., unschedule_txq checks if the txq being removed is currently being
pointed to by schedule_pos[ac], and if it is, it updates schedule_pos to
be the rb_next of the current value?
-Toke
