xfrm: Fix xfrm_policy_gc_lock handling.

From: Alexey Dobriyan <[e-mail]>

Based upon a lockdep trace by Simon Arlott.

xfrm_policy_kill() can be called from both BH and
non-BH contexts, so we have to grab xfrm_policy_gc_lock
with BH disabling.

Signed-off-by: David S. Miller <[e-mail]>

net/xfrm/xfrm_policy.c

···
 		return;
 	}
 
-	spin_lock(&xfrm_policy_gc_lock);
+	spin_lock_bh(&xfrm_policy_gc_lock);
 	hlist_add_head(&policy->bydst, &xfrm_policy_gc_list);
-	spin_unlock(&xfrm_policy_gc_lock);
+	spin_unlock_bh(&xfrm_policy_gc_lock);
 
 	schedule_work(&xfrm_policy_gc_work);
 }