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, 3 insertions, 2 deletions

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 3d7a2c0b836a..87be58673b55 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -328,6 +328,7 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
         int err;
         int is_udplite = IS_UDPLITE(sk);
         int is_udp4;
+        bool slow;
 
         if (addr_len)
                 *addr_len=sizeof(struct sockaddr_in6);
@@ -424,7 +425,7 @@ out:
         return err;
 
 csum_copy_err:
-        lock_sock_bh(sk);
+        slow = lock_sock_fast(sk);
         if (!skb_kill_datagram(sk, skb, flags)) {
                 if (is_udp4)
                         UDP_INC_STATS_USER(sock_net(sk),
@@ -433,7 +434,7 @@ csum_copy_err:
                         UDP6_INC_STATS_USER(sock_net(sk),
                                         UDP_MIB_INERRORS, is_udplite);
         }
-        unlock_sock_bh(sk);
+        unlock_sock_fast(sk, slow);
 
         if (flags & MSG_DONTWAIT)
                 return -EAGAIN;