linux-kernel - Re: [PATCH net-next] tcp: show number of network segments in some SNMP counters

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Date:   Mon, 10 Sep 2018 23:07:37 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     kbuild-all@...org, edumazet@...gle.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yafang Shao <laoar.shao@...il.com>
Subject: Re: [PATCH net-next] tcp: show number of network segments in some
 SNMP counters

Hi Yafang,

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/Yafang-Shao/tcp-show-number-of-network-segments-in-some-SNMP-counters/20180910-225108
config: x86_64-randconfig-x019-201836 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   In file included from net/ipv4/tcp_ipv4.c:69:0:
   net/ipv4/tcp_ipv4.c: In function 'tcp_v4_err':
>> include/net/tcp.h:917:24: warning: 'skb' may be used uninitialized in this function [-Wmaybe-uninitialized]
     return TCP_SKB_CB(skb)->tcp_gso_segs;
                           ^
   net/ipv4/tcp_ipv4.c:436:18: note: 'skb' was declared here
     struct sk_buff *skb;
                     ^~~
--
   In file included from net//ipv4/tcp_ipv4.c:69:0:
   net//ipv4/tcp_ipv4.c: In function 'tcp_v4_err':
>> include/net/tcp.h:917:24: warning: 'skb' may be used uninitialized in this function [-Wmaybe-uninitialized]
     return TCP_SKB_CB(skb)->tcp_gso_segs;
                           ^
   net//ipv4/tcp_ipv4.c:436:18: note: 'skb' was declared here
     struct sk_buff *skb;
                     ^~~

vim +/skb +917 include/net/tcp.h

3fa6f616 David Ahern    2017-08-07  911  
^1da177e Linus Torvalds 2005-04-16  912  /* Due to TSO, an SKB can be composed of multiple actual
^1da177e Linus Torvalds 2005-04-16  913   * packets.  To keep these tracked properly, we use this.
bd14b1b2 Eric Dumazet   2012-05-04  914   */
^1da177e Linus Torvalds 2005-04-16  915  static inline int tcp_skb_pcount(const struct sk_buff *skb)
bd14b1b2 Eric Dumazet   2012-05-04  916  {
cd7d8498 Eric Dumazet   2014-09-24 @917  	return TCP_SKB_CB(skb)->tcp_gso_segs;
cd7d8498 Eric Dumazet   2014-09-24  918  }
bd14b1b2 Eric Dumazet   2012-05-04  919  

:::::: The code at line 917 was first introduced by commit
:::::: cd7d8498c9a5d510c64db38d9f4f4fbc41790f09 tcp: change tcp_skb_pcount() location

:::::: TO: Eric Dumazet <edumazet@...gle.com>
:::::: CC: David S. Miller <davem@...emloft.net>

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