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    Subject[PATCH v1 6/8] dmaengine: enhance network subsystem to support DMA device hotplug
    Date
    Enhance network subsystem to correctly update DMA channel reference counts,
    so it won't break DMA device hotplug logic.

    Signed-off-by: Jiang Liu <liuj97@gmail.com>
    ---
    include/net/netdma.h | 26 ++++++++++++++++++++++++++
    net/ipv4/tcp.c | 10 +++-------
    net/ipv4/tcp_input.c | 5 +----
    net/ipv4/tcp_ipv4.c | 4 +---
    net/ipv6/tcp_ipv6.c | 4 +---
    5 files changed, 32 insertions(+), 17 deletions(-)

    diff --git a/include/net/netdma.h b/include/net/netdma.h
    index 8ba8ce2..6d71724 100644
    --- a/include/net/netdma.h
    +++ b/include/net/netdma.h
    @@ -24,6 +24,32 @@
    #include <linux/dmaengine.h>
    #include <linux/skbuff.h>

    +static inline bool
    +net_dma_capable(void)
    +{
    + struct dma_chan *chan = net_dma_find_channel();
    + dma_put_channel(chan);
    +
    + return !!chan;
    +}
    +
    +static inline struct dma_chan *
    +net_dma_get_channel(struct tcp_sock *tp)
    +{
    + if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
    + tp->ucopy.dma_chan = net_dma_find_channel();
    + return tp->ucopy.dma_chan;
    +}
    +
    +static inline void
    +net_dma_put_channel(struct tcp_sock *tp)
    +{
    + if (tp->ucopy.dma_chan) {
    + dma_put_channel(tp->ucopy.dma_chan);
    + tp->ucopy.dma_chan = NULL;
    + }
    +}
    +
    int dma_skb_copy_datagram_iovec(struct dma_chan* chan,
    struct sk_buff *skb, int offset, struct iovec *to,
    size_t len, struct dma_pinned_list *pinned_list);
    diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
    index 8bb6ade..aea4032 100644
    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -1451,8 +1451,7 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
    available = TCP_SKB_CB(skb)->seq + skb->len - (*seq);
    if ((available < target) &&
    (len > sysctl_tcp_dma_copybreak) && !(flags & MSG_PEEK) &&
    - !sysctl_tcp_low_latency &&
    - net_dma_find_channel()) {
    + !sysctl_tcp_low_latency && net_dma_capable()) {
    preempt_enable_no_resched();
    tp->ucopy.pinned_list =
    dma_pin_iovec_pages(msg->msg_iov, len);
    @@ -1666,10 +1665,7 @@ do_prequeue:

    if (!(flags & MSG_TRUNC)) {
    #ifdef CONFIG_NET_DMA
    - if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
    - tp->ucopy.dma_chan = net_dma_find_channel();
    -
    - if (tp->ucopy.dma_chan) {
    + if (net_dma_get_channel(tp)) {
    tp->ucopy.dma_cookie = dma_skb_copy_datagram_iovec(
    tp->ucopy.dma_chan, skb, offset,
    msg->msg_iov, used,
    @@ -1758,7 +1754,7 @@ skip_copy:

    #ifdef CONFIG_NET_DMA
    tcp_service_net_dma(sk, true); /* Wait for queue to drain */
    - tp->ucopy.dma_chan = NULL;
    + net_dma_put_channel(tp);

    if (tp->ucopy.pinned_list) {
    dma_unpin_iovec_pages(tp->ucopy.pinned_list);
    diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
    index 9944c1d..3878916 100644
    --- a/net/ipv4/tcp_input.c
    +++ b/net/ipv4/tcp_input.c
    @@ -5227,10 +5227,7 @@ static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
    if (tp->ucopy.wakeup)
    return 0;

    - if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
    - tp->ucopy.dma_chan = net_dma_find_channel();
    -
    - if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
    + if (net_dma_get_channel(tp) && skb_csum_unnecessary(skb)) {

    dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
    skb, hlen,
    diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
    index 0cb86ce..90ea1c0 100644
    --- a/net/ipv4/tcp_ipv4.c
    +++ b/net/ipv4/tcp_ipv4.c
    @@ -1729,9 +1729,7 @@ process:
    if (!sock_owned_by_user(sk)) {
    #ifdef CONFIG_NET_DMA
    struct tcp_sock *tp = tcp_sk(sk);
    - if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
    - tp->ucopy.dma_chan = net_dma_find_channel();
    - if (tp->ucopy.dma_chan)
    + if (net_dma_get_channel(tp))
    ret = tcp_v4_do_rcv(sk, skb);
    else
    #endif
    diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
    index 86cfe60..fb81bbd 100644
    --- a/net/ipv6/tcp_ipv6.c
    +++ b/net/ipv6/tcp_ipv6.c
    @@ -1644,9 +1644,7 @@ process:
    if (!sock_owned_by_user(sk)) {
    #ifdef CONFIG_NET_DMA
    struct tcp_sock *tp = tcp_sk(sk);
    - if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
    - tp->ucopy.dma_chan = net_dma_find_channel();
    - if (tp->ucopy.dma_chan)
    + if (net_dma_get_channel(tp))
    ret = tcp_v6_do_rcv(sk, skb);
    else
    #endif
    --
    1.7.5.4


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