ipvs: Fix possible deadlock in sync code

Commit 998e7a76804b7a273a0460c2cdd5a51fa9856717 ("ipvs: Use kthread_run()
instead of doing a double-fork via kernel_thread()") introduced a possible
deadlock in the sync code. We need to use the _bh versions for the lock, as the
lock is also accessed from a bottom half.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Acked-by: Simon Horman <horms@verge.net.au>

net/ipv4/ipvs/ip_vs_sync.c

@@ -904,9 +904,9 @@ int stop_sync_thread(int state)
 		 * progress of stopping the master sync daemon.
 		 */
 
-		spin_lock(&ip_vs_sync_lock);
+		spin_lock_bh(&ip_vs_sync_lock);
 		ip_vs_sync_state &= ~IP_VS_STATE_MASTER;
-		spin_unlock(&ip_vs_sync_lock);
+		spin_unlock_bh(&ip_vs_sync_lock);
 		kthread_stop(sync_master_thread);
 		sync_master_thread = NULL;
 	} else if (state == IP_VS_STATE_BACKUP) {