tcp: add memory barriers to write space paths
Ensure that we either see that the buffer has write space
in tcp_poll() or that we perform a wakeup from the input
side. Did not run into any actual problem here, but thought
that we should make things explicit.
Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 59c8a02..8c5cd9e 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -520,8 +520,10 @@
/* Race breaker. If space is freed after
* wspace test but before the flags are set,
- * IO signal will be lost.
+ * IO signal will be lost. Memory barrier
+ * pairs with the input side.
*/
+ smp_mb__after_atomic();
if (sk_stream_is_writeable(sk))
mask |= POLLOUT | POLLWRNORM;
}