netdev - Re: [PATCH net-next] tcp: force cwnd at least 2 in tcp_cwnd

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Message-ID: <201806271043.CAKP12NC%fengguang.wu@intel.com>
Date:   Wed, 27 Jun 2018 10:18:06 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Lawrence Brakmo <brakmo@...com>
Cc:     kbuild-all@...org, netdev <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Blake Matheny <bmatheny@...com>,
        Alexei Starovoitov <ast@...com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] tcp: force cwnd at least 2 in tcp_cwnd_reduction

Hi Lawrence,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Lawrence-Brakmo/tcp-force-cwnd-at-least-2-in-tcp_cwnd_reduction/20180627-095533
config: x86_64-randconfig-x003-201825 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   In file included from include/asm-generic/bug.h:18:0,
                    from arch/x86/include/asm/bug.h:83,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/mm.h:9,
                    from net/ipv4/tcp_input.c:67:
   net/ipv4/tcp_input.c: In function 'tcp_cwnd_reduction':
   include/linux/kernel.h:812:29: warning: comparison of distinct pointer types lacks a cast
      (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                                ^
   include/linux/kernel.h:826:4: note: in expansion of macro '__typecheck'
      (__typecheck(x, y) && __no_side_effects(x, y))
       ^~~~~~~~~~~
   include/linux/kernel.h:836:24: note: in expansion of macro '__safe_cmp'
     __builtin_choose_expr(__safe_cmp(x, y), \
                           ^~~~~~~~~~
   include/linux/kernel.h:852:19: note: in expansion of macro '__careful_cmp'
    #define max(x, y) __careful_cmp(x, y, >)
                      ^~~~~~~~~~~~~
>> net/ipv4/tcp_input.c:2480:17: note: in expansion of macro 'max'
     tp->snd_cwnd = max(tcp_packets_in_flight(tp) + sndcnt, 2);
                    ^~~

vim +/max +2480 net/ipv4/tcp_input.c

  2455	
  2456	void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
  2457	{
  2458		struct tcp_sock *tp = tcp_sk(sk);
  2459		int sndcnt = 0;
  2460		int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
  2461	
  2462		if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
  2463			return;
  2464	
  2465		tp->prr_delivered += newly_acked_sacked;
  2466		if (delta < 0) {
  2467			u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
  2468				       tp->prior_cwnd - 1;
  2469			sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
  2470		} else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
  2471			   !(flag & FLAG_LOST_RETRANS)) {
  2472			sndcnt = min_t(int, delta,
  2473				       max_t(int, tp->prr_delivered - tp->prr_out,
  2474					     newly_acked_sacked) + 1);
  2475		} else {
  2476			sndcnt = min(delta, newly_acked_sacked);
  2477		}
  2478		/* Force a fast retransmit upon entering fast recovery */
  2479		sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
> 2480		tp->snd_cwnd = max(tcp_packets_in_flight(tp) + sndcnt, 2);
  2481	}
  2482	

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