Re: hung task in mac80211

On Wed, 6 Sep 2017 13:57:47 +0200
Matteo Croce [off-list ref] wrote:

quoted

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