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, 14 insertions, 6 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index d2a71b04a5ae..ca241ea14875 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1026,15 +1026,23 @@ extern void release_sock(struct sock *sk);
                                 SINGLE_DEPTH_NESTING)
 #define bh_unlock_sock(__sk)    spin_unlock(&((__sk)->sk_lock.slock))
 
-static inline void lock_sock_bh(struct sock *sk)
+extern bool lock_sock_fast(struct sock *sk);
+/**
+ * unlock_sock_fast - complement of lock_sock_fast
+ * @sk: socket
+ * @slow: slow mode
+ *
+ * fast unlock socket for user context.
+ * If slow mode is on, we call regular release_sock()
+ */
+static inline void unlock_sock_fast(struct sock *sk, bool slow)
 {
-        spin_lock_bh(&sk->sk_lock.slock);
+        if (slow)
+                release_sock(sk);
+        else
+                spin_unlock_bh(&sk->sk_lock.slock);
 }
 
-static inline void unlock_sock_bh(struct sock *sk)
-{
-        spin_unlock_bh(&sk->sk_lock.slock);
-}
 
 extern struct sock              *sk_alloc(struct net *net, int family,
                                           gfp_t priority,