On Tue, Mar 26, 2019 at 11:35 AM Eric Dumazet <eduma...@google.com> wrote:
>
> My recent patch had at least three problems :
>
> 1) TX zerocopy wants notification when skb is acknowledged,
> thus we need to call skb_zcopy_clear() if the skb is
> cached into sk->sk_tx_skb_cache
>
> 2) Some applications might expect precise EPOLLOUT
> notifications, so we need to update sk->sk_wmem_queued
> and call sk_mem_uncharge() from sk_wmem_free_skb()
> in all cases. The SOCK_QUEUE_SHRUNK flag must also be set.
>
> 3) Reuse of saved skb should have used skb_cloned() instead
> of simply checking if the fast clone has been freed.
>
> Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Cc: Willem de Bruijn <will...@google.com>
> Cc: Soheil Hassas Yeganeh <soh...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
I can't think of other corner cases. Thanks!
> ---
> include/net/sock.h | 9 +++++----
> net/ipv4/tcp.c | 13 +++----------
> 2 files changed, 8 insertions(+), 14 deletions(-)
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index
> 577d91fb56267371c6bc5ae65f7454deba726bd6..7fa2232785226bcafd46b230559964fd16f3c4f4
> 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1465,13 +1465,14 @@ static inline void sk_mem_uncharge(struct sock *sk,
> int size)
>
> static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
> {
> - if (!sk->sk_tx_skb_cache) {
> - sk->sk_tx_skb_cache = skb;
> - return;
> - }
> sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
> sk->sk_wmem_queued -= skb->truesize;
> sk_mem_uncharge(sk, skb->truesize);
> + if (!sk->sk_tx_skb_cache) {
> + skb_zcopy_clear(skb, true);
> + sk->sk_tx_skb_cache = skb;
> + return;
> + }
> __kfree_skb(skb);
> }
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index
> 29b94edf05f9357d3a33744d677827ce624738ae..82bd707c03472f2cebb1a90d5f1c13acc821468f
> 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -865,14 +865,9 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int
> size, gfp_t gfp,
> {
> struct sk_buff *skb;
>
> - skb = sk->sk_tx_skb_cache;
> - if (skb && !size) {
> - const struct sk_buff_fclones *fclones;
> -
> - fclones = container_of(skb, struct sk_buff_fclones, skb1);
> - if (refcount_read(&fclones->fclone_ref) == 1) {
> - sk->sk_wmem_queued -= skb->truesize;
> - sk_mem_uncharge(sk, skb->truesize);
> + if (likely(!size)) {
> + skb = sk->sk_tx_skb_cache;
> + if (skb && !skb_cloned(skb)) {
> skb->truesize -= skb->data_len;
> sk->sk_tx_skb_cache = NULL;
> pskb_trim(skb, 0);
> @@ -2543,8 +2538,6 @@ void tcp_write_queue_purge(struct sock *sk)
> tcp_rtx_queue_purge(sk);
> skb = sk->sk_tx_skb_cache;
> if (skb) {
> - sk->sk_wmem_queued -= skb->truesize;
> - sk_mem_uncharge(sk, skb->truesize);
> __kfree_skb(skb);
> sk->sk_tx_skb_cache = NULL;
> }
> --
> 2.21.0.392.gf8f6787159e-goog
>
