On Tue, May 3, 2016 at 12:49 AM, Eric Dumazet <eric.duma...@gmail.com> wrote:
> From: Eric Dumazet <eduma...@google.com>
>
> Under high rx pressure, it is possible tcp_sendmsg() never has a
> chance to allocate an skb and loop forever as sk_flush_backlog()
> would always return true.
>
> Fix this by calling sk_flush_backlog() only if one skb had been
> allocated and filled before last backlog check.
>
> Fixes: d41a69f1d390 ("tcp: make tcp_sendmsg() aware of socket backlog")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
> ---
> net/ipv4/tcp.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index
> b945c2b046c5ead5503505f250c3c67761b284ae..5c7ed147449c1b7ba029b12e033ad779a631460a
> 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1084,6 +1084,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg,
> size_t size)
> struct sockcm_cookie sockc;
> int flags, err, copied = 0;
> int mss_now = 0, size_goal, copied_syn = 0;
> + bool process_backlog = false;
> bool sg;
> long timeo;
>
> @@ -1167,9 +1168,10 @@ new_segment:
> if (!sk_stream_memory_free(sk))
> goto wait_for_sndbuf;
>
> - if (sk_flush_backlog(sk))
> + if (process_backlog && sk_flush_backlog(sk)) {
> + process_backlog = false;
> goto restart;
> -
> + }
> skb = sk_stream_alloc_skb(sk,
> select_size(sk, sg),
> sk->sk_allocation,
> @@ -1177,6 +1179,7 @@ new_segment:
> if (!skb)
> goto wait_for_memory;
>
> + process_backlog = true;
> /*
> * Check whether we can use HW checksum.
> */
>
>
Nice catch! Thanks.
