Re: [PATCH net-next] tcp: add TCP_ECN and TCP_ECN_OPTION socket options

[kernel test robot <lkp@intel.com>]

Hi Irlanki,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 548b86839f7fb819a4d6c83b71c73ec378d24275]

url:    https://github.com/intel-lab-lkp/linux/commits/Irlanki-Sandeep/tcp-add-TCP_ECN-and-TCP_ECN_OPTION-socket-options/20260909-201557
base:   548b86839f7fb819a4d6c83b71c73ec378d24275
patch link:    https://lore.kernel.org/r/20260909144557.800676-1-irlanki.s%40samsung.com
patch subject: [PATCH net-next] tcp: add TCP_ECN and TCP_ECN_OPTION socket options
config: i386-randconfig-141-20260910 (https://download.01.org/0day-ci/archive/20260910/202609100957.cYRwpjGl-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.4.0-5) 12.4.0
smatch: v0.5.0-9187-g5189e3fb
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260910/202609100957.cYRwpjGl-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202609100957.cYRwpjGl-lkp@intel.com/

All warnings (new ones prefixed by >>):

   net/ipv4/tcp_input.c: In function 'tcp_ecn_create_request':
>> net/ipv4/tcp_input.c:7460:27: warning: unused variable 'net' [-Wunused-variable]
    7460 |         const struct net *net = sock_net(listen_sk);
         |                           ^~~


vim +/net +7460 net/ipv4/tcp_input.c

1fb6f159fd21c64 Octavian Purdila                      2014-06-25  7436  
d82bd1229885d55 Florian Westphal                      2014-09-29  7437  /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
d82bd1229885d55 Florian Westphal                      2014-09-29  7438   *
d82bd1229885d55 Florian Westphal                      2014-09-29  7439   * If we receive a SYN packet with these bits set, it means a
d82bd1229885d55 Florian Westphal                      2014-09-29  7440   * network is playing bad games with TOS bits. In order to
d82bd1229885d55 Florian Westphal                      2014-09-29  7441   * avoid possible false congestion notifications, we disable
f4e715c3254e3c0 stephen hemminger                     2014-10-29  7442   * TCP ECN negotiation.
d82bd1229885d55 Florian Westphal                      2014-09-29  7443   *
d82bd1229885d55 Florian Westphal                      2014-09-29  7444   * Exception: tcp_ca wants ECN. This is required for DCTCP
843c2fdf7a12951 Florian Westphal                      2015-01-30  7445   * congestion control: Linux DCTCP asserts ECT on all packets,
843c2fdf7a12951 Florian Westphal                      2015-01-30  7446   * including SYN, which is most optimal solution; however,
843c2fdf7a12951 Florian Westphal                      2015-01-30  7447   * others, such as FreeBSD do not.
f6fee16dbbe3fe4 Tilmans, Olivier (Nokia - BE/Antwerp  2019-04-03  7448)  *
f6fee16dbbe3fe4 Tilmans, Olivier (Nokia - BE/Antwerp  2019-04-03  7449)  * Exception: At least one of the reserved bits of the TCP header (th->res1) is
f6fee16dbbe3fe4 Tilmans, Olivier (Nokia - BE/Antwerp  2019-04-03  7450)  * set, indicating the use of a future TCP extension (such as AccECN). See
f6fee16dbbe3fe4 Tilmans, Olivier (Nokia - BE/Antwerp  2019-04-03  7451)  * RFC8311 §4.3 which updates RFC3168 to allow the development of such
f6fee16dbbe3fe4 Tilmans, Olivier (Nokia - BE/Antwerp  2019-04-03  7452)  * extensions.
d82bd1229885d55 Florian Westphal                      2014-09-29  7453   */
d82bd1229885d55 Florian Westphal                      2014-09-29  7454  static void tcp_ecn_create_request(struct request_sock *req,
d82bd1229885d55 Florian Westphal                      2014-09-29  7455  				   const struct sk_buff *skb,
f7b3bec6f5167ef Florian Westphal                      2014-11-03  7456  				   const struct sock *listen_sk,
f7b3bec6f5167ef Florian Westphal                      2014-11-03  7457  				   const struct dst_entry *dst)
d82bd1229885d55 Florian Westphal                      2014-09-29  7458  {
d82bd1229885d55 Florian Westphal                      2014-09-29  7459  	const struct tcphdr *th = tcp_hdr(skb);
d82bd1229885d55 Florian Westphal                      2014-09-29 @7460  	const struct net *net = sock_net(listen_sk);
d82bd1229885d55 Florian Westphal                      2014-09-29  7461  	bool th_ecn = th->ece && th->cwr;
843c2fdf7a12951 Florian Westphal                      2015-01-30  7462  	bool ect, ecn_ok;
c3a8d9474684d39 Daniel Borkmann                       2015-08-31  7463  	u32 ecn_ok_dst;
d82bd1229885d55 Florian Westphal                      2014-09-29  7464  
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7465  	if (tcp_accecn_syn_requested(th) &&
4ea2ce8e35e36ab Irlanki Sandeep                       2026-09-09  7466  	    (tcp_ecn_mode_eff(listen_sk) >= 3 ||
100f946b8d44b64 Chia-Yu Chang                         2026-01-31  7467  	     tcp_ca_needs_accecn(listen_sk))) {
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7468  		inet_rsk(req)->ecn_ok = 1;
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7469  		tcp_rsk(req)->accecn_ok = 1;
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7470  		tcp_rsk(req)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield &
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7471  					    INET_ECN_MASK;
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7472  		return;
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7473  	}
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7474  
d82bd1229885d55 Florian Westphal                      2014-09-29  7475  	if (!th_ecn)
d82bd1229885d55 Florian Westphal                      2014-09-29  7476  		return;
d82bd1229885d55 Florian Westphal                      2014-09-29  7477  
d82bd1229885d55 Florian Westphal                      2014-09-29  7478  	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
c3a8d9474684d39 Daniel Borkmann                       2015-08-31  7479  	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
4ea2ce8e35e36ab Irlanki Sandeep                       2026-09-09  7480  	ecn_ok = tcp_ecn_mode_eff(listen_sk) || ecn_ok_dst;
d82bd1229885d55 Florian Westphal                      2014-09-29  7481  
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7482  	if (((!ect || th->res1 || th->ae) && ecn_ok) ||
3cae34274c79e0c Ilpo Järvinen                         2025-09-16  7483  	    tcp_ca_needs_ecn(listen_sk) ||
91b5b21c7c16899 Lawrence Brakmo                       2017-06-30  7484  	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
91b5b21c7c16899 Lawrence Brakmo                       2017-06-30  7485  	    tcp_bpf_ca_needs_ecn((struct sock *)req))
d82bd1229885d55 Florian Westphal                      2014-09-29  7486  		inet_rsk(req)->ecn_ok = 1;
d82bd1229885d55 Florian Westphal                      2014-09-29  7487  }
d82bd1229885d55 Florian Westphal                      2014-09-29  7488  

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