Re: hung task in mac80211

[Matteo Croce]

On Wed, Sep 6, 2017 at 2:40 PM, Stefano Brivio <sbrivio@xxxxxxxxxx> wrote:
> On Wed, 6 Sep 2017 13:57:47 +0200
> Matteo Croce <mcroce@xxxxxxxxxx> wrote:
>
>> Hi,
>>
>> I have an hung task on vanilla 4.13 kernel which I haven't on 4.12.
>> The problem is present both on my AP and on my notebook,
>> so it seems it affects AP and STA mode as well.
>> The generated messages are:
>>
>> INFO: task kworker/u16:6:120 blocked for more than 120 seconds.
>>       Not tainted 4.13.0 #57
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> kworker/u16:6   D    0   120      2 0x00000000
>> Workqueue: phy0 ieee80211_ba_session_work [mac80211]
>> Call Trace:
>>  ? __schedule+0x174/0x5b0
>>  ? schedule+0x31/0x80
>>  ? schedule_preempt_disabled+0x9/0x10
>>  ? __mutex_lock.isra.2+0x163/0x480
>>  ? select_task_rq_fair+0xb9f/0xc60
>>  ? __ieee80211_start_rx_ba_session+0x135/0x4d0 [mac80211]
>>  ? __ieee80211_start_rx_ba_session+0x135/0x4d0 [mac80211]
>
> This is ugly and maybe wrong, but you could check perhaps...:
>
> diff --git a/net/mac80211/ht.c b/net/mac80211/ht.c
> index c92df492e898..bd7512a656f2 100644
> --- a/net/mac80211/ht.c
> +++ b/net/mac80211/ht.c
> @@ -320,28 +320,40 @@ void ieee80211_ba_session_work(struct work_struct *work)
>
>         mutex_lock(&sta->ampdu_mlme.mtx);
>         for (tid = 0; tid < IEEE80211_NUM_TIDS; tid++) {
> -               if (test_and_clear_bit(tid, sta->ampdu_mlme.tid_rx_timer_expired))
> +               if (test_and_clear_bit(tid, sta->ampdu_mlme.tid_rx_timer_expired)) {
> +                       mutex_unlock(&sta->ampdu_mlme.mtx);
>                         ___ieee80211_stop_rx_ba_session(
>                                 sta, tid, WLAN_BACK_RECIPIENT,
>                                 WLAN_REASON_QSTA_TIMEOUT, true);
> +                       mutex_lock(&sta->ampdu_mlme.mtx);
> +               }
>
>                 if (test_and_clear_bit(tid,
> -                                      sta->ampdu_mlme.tid_rx_stop_requested))
> +                                      sta->ampdu_mlme.tid_rx_stop_requested)) {
> +                       mutex_unlock(&sta->ampdu_mlme.mtx);
>                         ___ieee80211_stop_rx_ba_session(
>                                 sta, tid, WLAN_BACK_RECIPIENT,
>                                 WLAN_REASON_UNSPECIFIED, true);
> +                       mutex_lock(&sta->ampdu_mlme.mtx);
> +               }
>
>                 if (test_and_clear_bit(tid,
> -                                      sta->ampdu_mlme.tid_rx_manage_offl))
> +                                      sta->ampdu_mlme.tid_rx_manage_offl)) {
> +                       mutex_unlock(&sta->ampdu_mlme.mtx);
>                         __ieee80211_start_rx_ba_session(sta, 0, 0, 0, 1, tid,
>                                                         IEEE80211_MAX_AMPDU_BUF,
>                                                         false, true);
> +                       mutex_lock(&sta->ampdu_mlme.mtx);
> +               }
>
>                 if (test_and_clear_bit(tid + IEEE80211_NUM_TIDS,
> -                                      sta->ampdu_mlme.tid_rx_manage_offl))
> +                                      sta->ampdu_mlme.tid_rx_manage_offl)) {
> +                       mutex_unlock(&sta->ampdu_mlme.mtx);
>                         ___ieee80211_stop_rx_ba_session(
>                                 sta, tid, WLAN_BACK_RECIPIENT,
>                                 0, false);
> +                       mutex_lock(&sta->ampdu_mlme.mtx);
> +               }
>
>                 spin_lock_bh(&sta->lock);
>
> --
> Stefano
>

ACK, I have it running since 12 minutes.
The hang usually appears shortly after boot as I set
kernel.hung_task_timeout_secs=10

-- 
Matteo Croce
per aspera ad upstream