Re: [net-next] tcp: don't free a FIN sk_buff in tcp_remove_empty_skb()

[kernel test robot]

Hi Jon,

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/Jon-Maxwell/tcp-don-t-free-a-FIN-sk_buff-in-tcp_remove_empty_skb/20211021-072644
base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git 2641b62d2fab52648e34cdc6994b2eacde2d27c1
config: i386-randconfig-s002-20211021 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-dirty
        # https://github.com/0day-ci/linux/commit/87f5ea309107de5183ec0bd7d0b48ec90546d350
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Jon-Maxwell/tcp-don-t-free-a-FIN-sk_buff-in-tcp_remove_empty_skb/20211021-072644
        git checkout 87f5ea309107de5183ec0bd7d0b48ec90546d350
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>


sparse warnings: (new ones prefixed by >>)
>> net/ipv4/tcp.c:941:61: sparse: sparse: dubious: !x & y

vim +941 net/ipv4/tcp.c

0c54b85f282812 Ilpo Järvinen 2009-03-14  932
fdfc5c8594c24c Eric Dumazet  2019-08-26  933  /* In some cases, both sendpage() and sendmsg() could have added
fdfc5c8594c24c Eric Dumazet  2019-08-26  934   * an skb to the write queue, but failed adding payload on it.
fdfc5c8594c24c Eric Dumazet  2019-08-26  935   * We need to remove it to consume less memory, but more
fdfc5c8594c24c Eric Dumazet  2019-08-26  936   * importantly be able to generate EPOLLOUT for Edge Trigger epoll()
fdfc5c8594c24c Eric Dumazet  2019-08-26  937   * users.
fdfc5c8594c24c Eric Dumazet  2019-08-26  938   */
b796d04bd014fd Paolo Abeni   2020-11-16  939  void tcp_remove_empty_skb(struct sock *sk, struct sk_buff *skb)
fdfc5c8594c24c Eric Dumazet  2019-08-26  940  {
87f5ea309107de Jon Maxwell   2021-10-21 @941  	if (skb && !skb->len && !TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
fdfc5c8594c24c Eric Dumazet  2019-08-26  942  		tcp_unlink_write_queue(skb, sk);
fdfc5c8594c24c Eric Dumazet  2019-08-26  943  		if (tcp_write_queue_empty(sk))
fdfc5c8594c24c Eric Dumazet  2019-08-26  944  			tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
fdfc5c8594c24c Eric Dumazet  2019-08-26  945  		sk_wmem_free_skb(sk, skb);
fdfc5c8594c24c Eric Dumazet  2019-08-26  946  	}
fdfc5c8594c24c Eric Dumazet  2019-08-26  947  }
fdfc5c8594c24c Eric Dumazet  2019-08-26  948

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