llc: avoid blocking in llc_sap_close()

llc_sap_close() is called by llc_sap_put() which
could be called in BH context in llc_rcv(). We can't
block in BH.

There is no reason to block it here, kfree_rcu() should
be sufficient.

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

include/net/llc.h

···
 	int sk_count;
 	struct hlist_nulls_head sk_laddr_hash[LLC_SK_LADDR_HASH_ENTRIES];
 	struct hlist_head sk_dev_hash[LLC_SK_DEV_HASH_ENTRIES];
+	struct rcu_head rcu;
 };
 
 static inline

net/llc/llc_core.c

···
 	list_del_rcu(&sap->node);
 	spin_unlock_bh(&llc_sap_list_lock);
 
-	synchronize_rcu();
-
-	kfree(sap);
+	kfree_rcu(sap, rcu);
 }
 
 static struct packet_type llc_packet_type __read_mostly = {