Subject: Re: hung task in mac80211

From: Johannes Berg <[email-masked]>
Date: Wed, 06 Sep 2017 14:58:48 +0200

On Wed, 2017-09-06 at 13:57 +0200, Matteo Croce wrote:

> 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]

Yeah - obviously as Stefano found, both take &sta->ampdu_mlme.mtx.

Can you try this?

diff --git a/net/mac80211/agg-rx.c b/net/mac80211/agg-rx.c
index 2b36eff5d97e..d8d32776031e 100644
--- a/net/mac80211/agg-rx.c
+++ b/net/mac80211/agg-rx.c
@@ -245,10 +245,10 @@ static void ieee80211_send_addba_resp(struct ieee80211_sub_if_data *sdata, u8 *d
 	ieee80211_tx_skb(sdata, skb);
 }
 
-void __ieee80211_start_rx_ba_session(struct sta_info *sta,
-				     u8 dialog_token, u16 timeout,
-				     u16 start_seq_num, u16 ba_policy, u16 tid,
-				     u16 buf_size, bool tx, bool auto_seq)
+void ___ieee80211_start_rx_ba_session(struct sta_info *sta,
+				      u8 dialog_token, u16 timeout,
+				      u16 start_seq_num, u16 ba_policy, u16 tid,
+				      u16 buf_size, bool tx, bool auto_seq)
 {
 	struct ieee80211_local *local = sta->sdata->local;
 	struct tid_ampdu_rx *tid_agg_rx;
@@ -267,7 +267,7 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 		ht_dbg(sta->sdata,
 		       "STA %pM requests BA session on unsupported tid %d\n",
 		       sta->sta.addr, tid);
-		goto end_no_lock;
+		goto end;
 	}
 
 	if (!sta->sta.ht_cap.ht_supported) {
@@ -275,14 +275,14 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 		       "STA %pM erroneously requests BA session on tid %d w/o QoS\n",
 		       sta->sta.addr, tid);
 		/* send a response anyway, it's an error case if we get here */
-		goto end_no_lock;
+		goto end;
 	}
 
 	if (test_sta_flag(sta, WLAN_STA_BLOCK_BA)) {
 		ht_dbg(sta->sdata,
 		       "Suspend in progress - Denying ADDBA request (%pM tid %d)\n",
 		       sta->sta.addr, tid);
-		goto end_no_lock;
+		goto end;
 	}
 
 	/* sanity check for incoming parameters:
@@ -296,7 +296,7 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 		ht_dbg_ratelimited(sta->sdata,
 				   "AddBA Req with bad params from %pM on tid %u. policy %d, buffer size %d\n",
 				   sta->sta.addr, tid, ba_policy, buf_size);
-		goto end_no_lock;
+		goto end;
 	}
 	/* determine default buffer size */
 	if (buf_size == 0)
@@ -311,7 +311,6 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 	       buf_size, sta->sta.addr);
 
 	/* examine state machine */
-	mutex_lock(&sta->ampdu_mlme.mtx);
 
 	if (test_bit(tid, sta->ampdu_mlme.agg_session_valid)) {
 		if (sta->ampdu_mlme.tid_rx_token[tid] == dialog_token) {
@@ -415,15 +414,25 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 		__clear_bit(tid, sta->ampdu_mlme.unexpected_agg);
 		sta->ampdu_mlme.tid_rx_token[tid] = dialog_token;
 	}
-	mutex_unlock(&sta->ampdu_mlme.mtx);
 
-end_no_lock:
 	if (tx)
 		ieee80211_send_addba_resp(sta->sdata, sta->sta.addr, tid,
 					  dialog_token, status, 1, buf_size,
 					  timeout);
 }
 
+void __ieee80211_start_rx_ba_session(struct sta_info *sta,
+				     u8 dialog_token, u16 timeout,
+				     u16 start_seq_num, u16 ba_policy, u16 tid,
+				     u16 buf_size, bool tx, bool auto_seq)
+{
+	mutex_lock(&sta->ampdu_mlme.mtx);
+	___ieee80211_start_rx_ba_session(sta, dialog_token, timeout,
+					 start_seq_num, ba_policy, tid,
+					 buf_size, tx, auto_seq);
+	mutex_unlock(&sta->ampdu_mlme.mtx);
+}
+
 void ieee80211_process_addba_request(struct ieee80211_local *local,
 				     struct sta_info *sta,
 				     struct ieee80211_mgmt *mgmt,
diff --git a/net/mac80211/ht.c b/net/mac80211/ht.c
index c92df492e898..198b2d3e56fd 100644
--- a/net/mac80211/ht.c
+++ b/net/mac80211/ht.c
@@ -333,9 +333,9 @@ void ieee80211_ba_session_work(struct work_struct *work)
 
 		if (test_and_clear_bit(tid,
 				       sta->ampdu_mlme.tid_rx_manage_offl))
-			__ieee80211_start_rx_ba_session(sta, 0, 0, 0, 1, tid,
-							IEEE80211_MAX_AMPDU_BUF,
-							false, true);
+			___ieee80211_start_rx_ba_session(sta, 0, 0, 0, 1, tid,
+							 IEEE80211_MAX_AMPDU_BUF,
+							 false, true);
 
 		if (test_and_clear_bit(tid + IEEE80211_NUM_TIDS,
 				       sta->ampdu_mlme.tid_rx_manage_offl))
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 2197c62a0a6e..9675814f64db 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1760,6 +1760,10 @@ void __ieee80211_start_rx_ba_session(struct sta_info *sta,
 				     u8 dialog_token, u16 timeout,
 				     u16 start_seq_num, u16 ba_policy, u16 tid,
 				     u16 buf_size, bool tx, bool auto_seq);
+void ___ieee80211_start_rx_ba_session(struct sta_info *sta,
+				      u8 dialog_token, u16 timeout,
+				      u16 start_seq_num, u16 ba_policy, u16 tid,
+				      u16 buf_size, bool tx, bool auto_seq);
 void ieee80211_sta_tear_down_BA_sessions(struct sta_info *sta,
 					 enum ieee80211_agg_stop_reason reason);
 void ieee80211_process_delba(struct ieee80211_sub_if_data *sdata,

johannes