[NETPOLL]: tx lock deadlock fix

If sky2 device poll routine is called from netpoll_send_skb, it would
deadlock. The netpoll_send_skb held the netif_tx_lock, and the poll
routine could acquire it to clean up skb's. Other drivers might use
same locking model.

The driver is correct, netpoll should not introduce more locking
problems than it causes already. So change the code to drop lock
before calling poll handler.

Signed-off-by: Stephen Hemminger <shemminger@linux.foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 758dafe284c026acc0bf180a260cd9fe7626b750..f8e74e511ce63c57f0f1ab473a451c32f9965d06 100644 (file)
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -250,22 +250,23 @@ static void netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
                unsigned long flags;
 
                local_irq_save(flags);
-               if (netif_tx_trylock(dev)) {
-                       /* try until next clock tick */
-                       for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
-                                       tries > 0; --tries) {
+               /* try until next clock tick */
+               for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
+                    tries > 0; --tries) {
+                       if (netif_tx_trylock(dev)) {
                                if (!netif_queue_stopped(dev))
                                        status = dev->hard_start_xmit(skb, dev);
+                               netif_tx_unlock(dev);
 
                                if (status == NETDEV_TX_OK)
                                        break;
 
-                               /* tickle device maybe there is some cleanup */
-                               netpoll_poll(np);
-
-                               udelay(USEC_PER_POLL);
                        }
-                       netif_tx_unlock(dev);
+
+                       /* tickle device maybe there is some cleanup */
+                       netpoll_poll(np);
+
+                       udelay(USEC_PER_POLL);
                }
                local_irq_restore(flags);
        }