net: fix lock_sock_bh/unlock_sock_bh

This new sock lock primitive was introduced to speedup some user context
socket manipulation. But it is unsafe to protect two threads, one using
regular lock_sock/release_sock, one using lock_sock_bh/unlock_sock_bh

This patch changes lock_sock_bh to be careful against 'owned' state.
If owned is found to be set, we must take the slow path.
lock_sock_bh() now returns a boolean to say if the slow path was taken,
and this boolean is used at unlock_sock_bh time to call the appropriate
unlock function.

After this change, BH are either disabled or enabled during the
lock_sock_bh/unlock_sock_bh protected section. This might be misleading,
so we rename these functions to lock_sock_fast()/unlock_sock_fast().

Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 6 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 9de6a698f91d..b9d0d409516f 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1063,10 +1063,11 @@ static unsigned int first_packet_length(struct sock *sk)
         spin_unlock_bh(&rcvq->lock);
 
         if (!skb_queue_empty(&list_kill)) {
-                lock_sock_bh(sk);
+                bool slow = lock_sock_fast(sk);
+
                 __skb_queue_purge(&list_kill);
                 sk_mem_reclaim_partial(sk);
-                unlock_sock_bh(sk);
+                unlock_sock_fast(sk, slow);
         }
         return res;
 }
@@ -1123,6 +1124,7 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
         int peeked;
         int err;
         int is_udplite = IS_UDPLITE(sk);
+        bool slow;
 
         /*
          *      Check any passed addresses
@@ -1197,10 +1199,10 @@ out:
         return err;
 
 csum_copy_err:
-        lock_sock_bh(sk);
+        slow = lock_sock_fast(sk);
         if (!skb_kill_datagram(sk, skb, flags))
                 UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
-        unlock_sock_bh(sk);
+        unlock_sock_fast(sk, slow);
 
         if (noblock)
                 return -EAGAIN;
@@ -1625,9 +1627,9 @@ int udp_rcv(struct sk_buff *skb)
 
 void udp_destroy_sock(struct sock *sk)
 {
-        lock_sock_bh(sk);
+        bool slow = lock_sock_fast(sk);
         udp_flush_pending_frames(sk);
-        unlock_sock_bh(sk);
+        unlock_sock_fast(sk, slow);
 }
 
 /*