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Commit 3c715127 authored Apr 20, 2015 by jbaron@akamai.com Committed by David S. Miller Apr 21, 2015

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>

parent 71cd26e7

net/ipv4/tcp.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -520,8 +520,10 @@ unsigned int tcp_poll(struct file file, struct socket sock, poll_table *wait)

		/* 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;
		}

net/ipv4/tcp_input.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -4845,6 +4845,8 @@ static void tcp_check_space(struct sock *sk)
		{
		if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
		/* pairs with tcp_poll() */
		smp_mb__after_atomic();
		if (sk->sk_socket &&
		test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
		tcp_new_space(sk);