net: skb_free_datagram_locked() fix

Commit 4b0b72f7dd617b ( net: speedup udp receive path )
introduced a bug in skb_free_datagram_locked().

We should not skb_orphan() skb if we dont have the guarantee we are the
last skb user, this might happen with MSG_PEEK concurrent users.

To keep socket locked for the smallest period of time, we split
consume_skb() logic, inlined in skb_free_datagram_locked()

Reported-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 2 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 95b851f3d713..e0097531417a 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -229,13 +229,18 @@ EXPORT_SYMBOL(skb_free_datagram);
 
 void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
 {
+        if (likely(atomic_read(&skb->users) == 1))
+                smp_rmb();
+        else if (likely(!atomic_dec_and_test(&skb->users)))
+                return;
+
         lock_sock_bh(sk);
         skb_orphan(skb);
         sk_mem_reclaim_partial(sk);
         unlock_sock_bh(sk);
 
-        /* skb is now orphaned, might be freed outside of locked section */
-        consume_skb(skb);
+        /* skb is now orphaned, can be freed outside of locked section */
+        __kfree_skb(skb);
 }
 EXPORT_SYMBOL(skb_free_datagram_locked);