wifi: rtlwifi: rtl8723be: don't call kfree_skb() under spin_lock_irqsave()

It is not allowed to call kfree_skb() from hardware interrupt
context or with interrupts being disabled. All the SKBs have
been dequeued from the old queue, so it's safe to enqueue these
SKBs to a free queue, then free them after spin_unlock_irqrestore()
at once. Compile tested only.

Fixes: 5c99f04f ("rtlwifi: rtl8723be: Update driver to match Realtek release of 06/28/14")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221207141411.46098-4-yangyingliang@huawei.com

drivers/net/wireless/realtek/rtlwifi/rtl8723be/hw.c

@@ -30,8 +30,10 @@ static void _rtl8723be_return_beacon_queue_skb(struct ieee80211_hw *hw)
 	struct rtl_priv *rtlpriv = rtl_priv(hw);
 	struct rtl_pci *rtlpci = rtl_pcidev(rtl_pcipriv(hw));
 	struct rtl8192_tx_ring *ring = &rtlpci->tx_ring[BEACON_QUEUE];
+	struct sk_buff_head free_list;
 	unsigned long flags;
 
+	skb_queue_head_init(&free_list);
 	spin_lock_irqsave(&rtlpriv->locks.irq_th_lock, flags);
 	while (skb_queue_len(&ring->queue)) {
 		struct rtl_tx_desc *entry = &ring->desc[ring->idx];
@@ -41,10 +43,12 @@ static void _rtl8723be_return_beacon_queue_skb(struct ieee80211_hw *hw)
 				 rtlpriv->cfg->ops->get_desc(hw, (u8 *)entry,
 						true, HW_DESC_TXBUFF_ADDR),
 				 skb->len, DMA_TO_DEVICE);
-		kfree_skb(skb);
+		__skb_queue_tail(&free_list, skb);
 		ring->idx = (ring->idx + 1) % ring->entries;
 	}
 	spin_unlock_irqrestore(&rtlpriv->locks.irq_th_lock, flags);
+
+	__skb_queue_purge(&free_list);
 }
 
 static void _rtl8723be_set_bcn_ctrl_reg(struct ieee80211_hw *hw,