Commit 15c04175 authored Sep 14, 2012 by Michal Kubeček Committed by David S. Miller Sep 19, 2012

tcp: flush DMA queue before sk_wait_data if rcv_wnd is zero



If recv() syscall is called for a TCP socket so that
  - IOAT DMA is used
  - MSG_WAITALL flag is used
  - requested length is bigger than sk_rcvbuf
  - enough data has already arrived to bring rcv_wnd to zero
then when tcp_recvmsg() gets to calling sk_wait_data(), receive
window can be still zero while sk_async_wait_queue exhausts
enough space to keep it zero. As this queue isn't cleaned until
the tcp_service_net_dma() call, sk_wait_data() cannot receive
any data and blocks forever.

If zero receive window and non-empty sk_async_wait_queue is
detected before calling sk_wait_data(), process the queue first.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent dbd6b11e

net/ipv4/tcp.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -1762,8 +1762,14 @@ int tcp_recvmsg(struct kiocb iocb, struct sock sk, struct msghdr *msg,
		}

		#ifdef CONFIG_NET_DMA
		if (tp->ucopy.dma_chan)
		if (tp->ucopy.dma_chan) {
		if (tp->rcv_wnd == 0 &&
		!skb_queue_empty(&sk->sk_async_wait_queue)) {
		tcp_service_net_dma(sk, true);
		tcp_cleanup_rbuf(sk, copied);
		} else
		dma_async_memcpy_issue_pending(tp->ucopy.dma_chan);
		}
		#endif
		if (copied >= target) {
		/* Do not sleep, just process backlog. */

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