rds: Make rds_sock_lock BH rather than IRQ safe.

rds_sock_info() triggers locking warnings because we try to perform a
local_bh_enable() (via sock_i_ino()) while hardware interrupts are
disabled (via taking rds_sock_lock).

There is no reason for rds_sock_lock to be a hardware IRQ disabling
lock, none of these access paths run in hardware interrupt context.

Therefore making it a BH disabling lock is safe and sufficient to
fix this bug.

Reported-by: Kumar Sanghvi <[e-mail]>
Reported-by: Josh Boyer <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/rds/af_rds.c

···
 {
 	struct sock *sk = sock->sk;
 	struct rds_sock *rs;
-	unsigned long flags;
 
 	if (!sk)
 		goto out;
···
 	rds_rdma_drop_keys(rs);
 	rds_notify_queue_get(rs, NULL);
 
-	spin_lock_irqsave(&rds_sock_lock, flags);
+	spin_lock_bh(&rds_sock_lock);
 	list_del_init(&rs->rs_item);
 	rds_sock_count--;
-	spin_unlock_irqrestore(&rds_sock_lock, flags);
+	spin_unlock_bh(&rds_sock_lock);
 
 	rds_trans_put(rs->rs_transport);
 
···
 
 static int __rds_create(struct socket *sock, struct sock *sk, int protocol)
 {
-	unsigned long flags;
 	struct rds_sock *rs;
 
 	sock_init_data(sock, sk);
···
 	spin_lock_init(&rs->rs_rdma_lock);
 	rs->rs_rdma_keys = RB_ROOT;
 
-	spin_lock_irqsave(&rds_sock_lock, flags);
+	spin_lock_bh(&rds_sock_lock);
 	list_add_tail(&rs->rs_item, &rds_sock_list);
 	rds_sock_count++;
-	spin_unlock_irqrestore(&rds_sock_lock, flags);
+	spin_unlock_bh(&rds_sock_lock);
 
 	return 0;
 }
···
 {
 	struct rds_sock *rs;
 	struct rds_incoming *inc;
-	unsigned long flags;
 	unsigned int total = 0;
 
 	len /= sizeof(struct rds_info_message);
 
-	spin_lock_irqsave(&rds_sock_lock, flags);
+	spin_lock_bh(&rds_sock_lock);
 
 	list_for_each_entry(rs, &rds_sock_list, rs_item) {
 		read_lock(&rs->rs_recv_lock);
···
 		read_unlock(&rs->rs_recv_lock);
 	}
 
-	spin_unlock_irqrestore(&rds_sock_lock, flags);
+	spin_unlock_bh(&rds_sock_lock);
 
 	lens->nr = total;
 	lens->each = sizeof(struct rds_info_message);
···
 {
 	struct rds_info_socket sinfo;
 	struct rds_sock *rs;
-	unsigned long flags;
 
 	len /= sizeof(struct rds_info_socket);
 
-	spin_lock_irqsave(&rds_sock_lock, flags);
+	spin_lock_bh(&rds_sock_lock);
 
 	if (len < rds_sock_count)
 		goto out;
···
 	lens->nr = rds_sock_count;
 	lens->each = sizeof(struct rds_info_socket);
 
-	spin_unlock_irqrestore(&rds_sock_lock, flags);
+	spin_unlock_bh(&rds_sock_lock);
 }
 
 static void rds_exit(void)