atm: solos-pci: Fix potential deadlock on &tx_queue_lock

As &card->tx_queue_lock is acquired under softirq context along the
following call chain from solos_bh(), other acquisition of the same
lock inside process context should disable at least bh to avoid double
lock.

<deadlock #2>
pclose()
--> spin_lock(&card->tx_queue_lock)
<interrupt>
--> solos_bh()
--> fpga_tx()
--> spin_lock(&card->tx_queue_lock)

This flaw was found by an experimental static analysis tool I am
developing for irq-related deadlock.

To prevent the potential deadlock, the patch uses spin_lock_bh()
on &card->tx_queue_lock under process context code consistently to
prevent the possible deadlock scenario.

Fixes: 213e85d38912 ("solos-pci: clean up pclose() function")
Signed-off-by: Chengfeng Ye <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/atm/solos-pci.c

···
 	struct pkt_hdr *header;
 
 	/* Remove any yet-to-be-transmitted packets from the pending queue */
-	spin_lock(&card->tx_queue_lock);
+	spin_lock_bh(&card->tx_queue_lock);
 	skb_queue_walk_safe(&card->tx_queue[port], skb, tmpskb) {
 		if (SKB_CB(skb)->vcc == vcc) {
 			skb_unlink(skb, &card->tx_queue[port]);
 			solos_pop(vcc, skb);
 		}
 	}
-	spin_unlock(&card->tx_queue_lock);
+	spin_unlock_bh(&card->tx_queue_lock);
 
 	skb = alloc_skb(sizeof(*header), GFP_KERNEL);
 	if (!skb) {