mISDN: hfcpci: don't call dev_kfree_skb/kfree_skb() under spin_lock_irqsave()

It is not allowed to call kfree_skb() or consume_skb() from hardware
interrupt context or with hardware interrupts being disabled.

skb_queue_purge() is called under spin_lock_irqsave() in hfcpci_l2l1D(),
kfree_skb() is called in it, to fix this, use skb_queue_splice_init()
to move the dch->squeue to a free queue, also enqueue the tx_skb and
rx_skb, at last calling __skb_queue_purge() to free the SKBs afer unlock.

Fixes: 1700fe1a ("Add mISDN HFC PCI driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/isdn/hardware/mISDN/hfcpci.c

@@ -1617,16 +1617,19 @@ hfcpci_l2l1D(struct mISDNchannel *ch, struct sk_buff *skb)
 		test_and_clear_bit(FLG_L2_ACTIVATED, &dch->Flags);
 		spin_lock_irqsave(&hc->lock, flags);
 		if (hc->hw.protocol == ISDN_P_NT_S0) {
+			struct sk_buff_head free_queue;
+
+			__skb_queue_head_init(&free_queue);
 			/* prepare deactivation */
 			Write_hfc(hc, HFCPCI_STATES, 0x40);
-			skb_queue_purge(&dch->squeue);
+			skb_queue_splice_init(&dch->squeue, &free_queue);
 			if (dch->tx_skb) {
-				dev_kfree_skb(dch->tx_skb);
+				__skb_queue_tail(&free_queue, dch->tx_skb);
 				dch->tx_skb = NULL;
 			}
 			dch->tx_idx = 0;
 			if (dch->rx_skb) {
-				dev_kfree_skb(dch->rx_skb);
+				__skb_queue_tail(&free_queue, dch->rx_skb);
 				dch->rx_skb = NULL;
 			}
 			test_and_clear_bit(FLG_TX_BUSY, &dch->Flags);
@@ -1639,10 +1642,12 @@ hfcpci_l2l1D(struct mISDNchannel *ch, struct sk_buff *skb)
 			hc->hw.mst_m &= ~HFCPCI_MASTER;
 			Write_hfc(hc, HFCPCI_MST_MODE, hc->hw.mst_m);
 			ret = 0;
+			spin_unlock_irqrestore(&hc->lock, flags);
+			__skb_queue_purge(&free_queue);
 		} else {
 			ret = l1_event(dch->l1, hh->prim);
-		}
 			spin_unlock_irqrestore(&hc->lock, flags);
+		}
 		break;
 	}
 	if (!ret)