rtw89: fix RCU usage in rtw89_core_txq_push()

ieee80211_tx_h_select_key() is performing a series of RCU dereferences,
but rtw89_core_txq_push() is calling it (via ieee80211_tx_dequeue_ni())
without RCU read-side lock held; fix that.

This addresses the splat below.

 =============================
 WARNING: suspicious RCU usage
 5.17.0-rc4-00003-gccad664b7f14 #3 Tainted: G            E
 -----------------------------
 net/mac80211/tx.c:593 suspicious rcu_dereference_check() usage!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by kworker/u33:0/184:
  #0: ffff9c0b14811d38 ((wq_completion)rtw89_tx_wq){+.+.}-{0:0}, at: process_one_work+0x258/0x660
  #1: ffffb97380cf3e78 ((work_completion)(&rtwdev->txq_work)){+.+.}-{0:0}, at: process_one_work+0x258/0x660

 stack backtrace:
 CPU: 8 PID: 184 Comm: kworker/u33:0 Tainted: G            E     5.17.0-rc4-00003-gccad664b7f14 #3 473b49ab0e7c2d6af2900c756bfd04efd7a9de13
 Hardware name: LENOVO 20UJS2B905/20UJS2B905, BIOS R1CET63W(1.32 ) 04/09/2021
 Workqueue: rtw89_tx_wq rtw89_core_txq_work [rtw89_core]
 Call Trace:
  <TASK>
  dump_stack_lvl+0x58/0x71
  ieee80211_tx_h_select_key+0x2c0/0x530 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  ieee80211_tx_dequeue+0x1a7/0x1260 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  rtw89_core_txq_work+0x1a6/0x420 [rtw89_core b39ba493f2e517ad75e0f8187ecc24edf58bbbea]
  process_one_work+0x2d8/0x660
  worker_thread+0x39/0x3e0
  ? process_one_work+0x660/0x660
  kthread+0xe5/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x22/0x30
  </TASK>

 =============================
 WARNING: suspicious RCU usage
 5.17.0-rc4-00003-gccad664b7f14 #3 Tainted: G            E
 -----------------------------
 net/mac80211/tx.c:607 suspicious rcu_dereference_check() usage!

 other info that might help us debug this:

 rcu_scheduler_active = 2, debug_locks = 1
 2 locks held by kworker/u33:0/184:
  #0: ffff9c0b14811d38 ((wq_completion)rtw89_tx_wq){+.+.}-{0:0}, at: process_one_work+0x258/0x660
  #1: ffffb97380cf3e78 ((work_completion)(&rtwdev->txq_work)){+.+.}-{0:0}, at: process_one_work+0x258/0x660

 stack backtrace:
 CPU: 8 PID: 184 Comm: kworker/u33:0 Tainted: G            E     5.17.0-rc4-00003-gccad664b7f14 #3 473b49ab0e7c2d6af2900c756bfd04efd7a9de13
 Hardware name: LENOVO 20UJS2B905/20UJS2B905, BIOS R1CET63W(1.32 ) 04/09/2021
 Workqueue: rtw89_tx_wq rtw89_core_txq_work [rtw89_core]
 Call Trace:
  <TASK>
  dump_stack_lvl+0x58/0x71
  ieee80211_tx_h_select_key+0x464/0x530 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  ieee80211_tx_dequeue+0x1a7/0x1260 [mac80211 911c23e2351c0ae60b597a67b1204a5ea955e365]
  rtw89_core_txq_work+0x1a6/0x420 [rtw89_core b39ba493f2e517ad75e0f8187ecc24edf58bbbea]
  process_one_work+0x2d8/0x660
  worker_thread+0x39/0x3e0
  ? process_one_work+0x660/0x660
  kthread+0xe5/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x22/0x30
  </TASK>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/nycvar.YFH.7.76.2202152037000.11721@cbobk.fhfr.pm

drivers/net/wireless/realtek/rtw89/core.c

@@ -1669,11 +1669,12 @@ static void rtw89_core_txq_push(struct rtw89_dev *rtwdev,
 	unsigned long i;
 	int ret;
 
+	rcu_read_lock();
 	for (i = 0; i < frame_cnt; i++) {
 		skb = ieee80211_tx_dequeue_ni(rtwdev->hw, txq);
 		if (!skb) {
 			rtw89_debug(rtwdev, RTW89_DBG_TXRX, "dequeue a NULL skb\n");
-			return;
+			goto out;
 		}
 		rtw89_core_txq_check_agg(rtwdev, rtwtxq, skb);
 		ret = rtw89_core_tx_write(rtwdev, vif, sta, skb, NULL);
@@ -1683,6 +1684,8 @@ static void rtw89_core_txq_push(struct rtw89_dev *rtwdev,
 			break;
 		}
 	}
+out:
+	rcu_read_unlock();
 }
 
 static u32 rtw89_check_and_reclaim_tx_resource(struct rtw89_dev *rtwdev, u8 tid)