target/linux/generic/backport-4.9/024-2-tcp-tsq-remove-one-locked-operation-in-tcp_wfree.patch

   1 From 408f0a6c21e124cc4f6c7aa370b38aa47e55428d Mon Sep 17 00:00:00 2001
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Sat, 3 Dec 2016 11:14:51 -0800
   4 Subject: [PATCH 02/10] tcp: tsq: remove one locked operation in tcp_wfree()
   5
   6 Instead of atomically clear TSQ_THROTTLED and atomically set TSQ_QUEUED
   7 bits, use one cmpxchg() to perform a single locked operation.
   8
   9 Since the following patch will also set TCP_TSQ_DEFERRED here,
  10 this cmpxchg() will make this addition free.
  11
  12 Signed-off-by: Eric Dumazet <edumazet@google.com>
  13 Signed-off-by: David S. Miller <davem@davemloft.net>
  14 ---
  15  net/ipv4/tcp_output.c | 13 ++++++++++---
  16  1 file changed, 10 insertions(+), 3 deletions(-)
  17
  18 --- a/net/ipv4/tcp_output.c
  19 +++ b/net/ipv4/tcp_output.c
  20 @@ -866,6 +866,7 @@ void tcp_wfree(struct sk_buff *skb)
  21  {
  22         struct sock *sk = skb->sk;
  23         struct tcp_sock *tp = tcp_sk(sk);
  24 +       unsigned long flags, nval, oval;
  25         int wmem;
  26
  27         /* Keep one reference on sk_wmem_alloc.
  28 @@ -883,11 +884,17 @@ void tcp_wfree(struct sk_buff *skb)
  29         if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
  30                 goto out;
  31
  32 -       if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
  33 -           !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
  34 -               unsigned long flags;
  35 +       for (oval = READ_ONCE(tp->tsq_flags);; oval = nval) {
  36                 struct tsq_tasklet *tsq;
  37
  38 +               if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
  39 +                       goto out;
  40 +
  41 +               nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED;
  42 +               nval = cmpxchg(&tp->tsq_flags, oval, nval);
  43 +               if (nval != oval)
  44 +                       continue;
  45 +
  46                 /* queue this socket to tasklet queue */
  47                 local_irq_save(flags);
  48                 tsq = this_cpu_ptr(&tsq_tasklet);