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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>
This commit is contained in:
Michal Kubeček 2012-09-14 04:59:52 +00:00 committed by David S. Miller
parent dbd6b11e15
commit 15c041759b
1 changed files with 8 additions and 2 deletions
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10
net/ipv4/tcp.c
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@ -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)
dma_async_memcpy_issue_pending(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. */