packet: fix warnings in rollover lock contention

Avoid two xchg calls whose return values were unused, causing a
warning on some architectures.

The relevant variable is a hint and read without mutual exclusion.
This fix makes all writers hold the receive_queue lock.

Suggested-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 10 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 31d58565726c..c30d14781576 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1301,17 +1301,12 @@ static int packet_rcv_has_room(struct packet_sock *po, struct sk_buff *skb)
         int ret;
         bool has_room;
 
-        if (po->prot_hook.func == tpacket_rcv) {
-                spin_lock(&po->sk.sk_receive_queue.lock);
-                ret = __packet_rcv_has_room(po, skb);
-                spin_unlock(&po->sk.sk_receive_queue.lock);
-        } else {
-                ret = __packet_rcv_has_room(po, skb);
-        }
-
+        spin_lock_bh(&po->sk.sk_receive_queue.lock);
+        ret = __packet_rcv_has_room(po, skb);
         has_room = ret == ROOM_NORMAL;
         if (po->pressure == has_room)
-                xchg(&po->pressure, !has_room);
+                po->pressure = !has_room;
+        spin_unlock_bh(&po->sk.sk_receive_queue.lock);
 
         return ret;
 }
@@ -3814,7 +3809,7 @@ static unsigned int packet_poll(struct file *file, struct socket *sock,
                         mask |= POLLIN | POLLRDNORM;
         }
         if (po->pressure && __packet_rcv_has_room(po, NULL) == ROOM_NORMAL)
-                xchg(&po->pressure, 0);
+                po->pressure = 0;
         spin_unlock_bh(&sk->sk_receive_queue.lock);
         spin_lock_bh(&sk->sk_write_queue.lock);
         if (po->tx_ring.pg_vec) {