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

[ Upstream commit d5dba32b8f6cb39be708b726044ba30dbc088b30 ]

As &card->cli_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 #1>
console_show()
--> spin_lock(&card->cli_queue_lock)
<interrupt>
   --> solos_bh()
   --> spin_lock(&card->cli_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 the card->cli_queue_lock under process context code consistently
to prevent the possible deadlock scenario.

Fixes: 9c54004 ("atm: Driver for Solos PCI ADSL2+ card.")
Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/atm/solos-pci.c

@@ -458,9 +458,9 @@ static ssize_t console_show(struct device *dev, struct device_attribute *attr,
 	struct sk_buff *skb;
 	unsigned int len;
 
-	spin_lock(&card->cli_queue_lock);
+	spin_lock_bh(&card->cli_queue_lock);
 	skb = skb_dequeue(&card->cli_queue[SOLOS_CHAN(atmdev)]);
-	spin_unlock(&card->cli_queue_lock);
+	spin_unlock_bh(&card->cli_queue_lock);
 	if(skb == NULL)
 		return sprintf(buf, "No data.\n");