netdev - Re: [PATCH net] ipmr: fix error path when mr_table

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Date:   Tue, 5 Jun 2018 15:29:46 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
Cc:     kbuild-all@...org, netdev@...r.kernel.org,
        Sabrina Dubroca <sd@...asysnail.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Yuval Mintz <yuvalm@...lanox.com>,
        Ivan Vecera <ivecera@...hat.com>
Subject: Re: [PATCH net] ipmr: fix error path when mr_table_alloc fails

Hi Sabrina,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net/master]

url:    https://github.com/0day-ci/linux/commits/Sabrina-Dubroca/ipmr-fix-error-path-when-mr_table_alloc-fails/20180605-060837
config: x86_64-randconfig-x006-201822 (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 

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 arch/x86/include/asm/current.h:5:0,
                    from include/linux/sched.h:12,
                    from include/linux/uaccess.h:5,
                    from net/ipv6/ip6mr.c:19:
   net/ipv6/ip6mr.c: In function 'ip6_mroute_setsockopt':
>> include/linux/compiler.h:177:26: warning: 'mrt' may be used uninitialized in this function [-Wmaybe-uninitialized]
     case 8: *(__u64 *)res = *(volatile __u64 *)p; break;  \
                             ^
   net/ipv6/ip6mr.c:1751:20: note: 'mrt' was declared here
      struct mr_table *mrt;
                       ^~~
--
   In file included from arch/x86/include/asm/current.h:5:0,
                    from include/linux/sched.h:12,
                    from include/linux/uaccess.h:5,
                    from net//ipv6/ip6mr.c:19:
   net//ipv6/ip6mr.c: In function 'ip6_mroute_setsockopt':
>> include/linux/compiler.h:177:26: warning: 'mrt' may be used uninitialized in this function [-Wmaybe-uninitialized]
     case 8: *(__u64 *)res = *(volatile __u64 *)p; break;  \
                             ^
   net//ipv6/ip6mr.c:1751:20: note: 'mrt' was declared here
      struct mr_table *mrt;
                       ^~~

vim +/mrt +177 include/linux/compiler.h

230fa253 Christian Borntraeger 2014-11-25  170  
d976441f Andrey Ryabinin       2015-10-19  171  #define __READ_ONCE_SIZE						\
d976441f Andrey Ryabinin       2015-10-19  172  ({									\
d976441f Andrey Ryabinin       2015-10-19  173  	switch (size) {							\
d976441f Andrey Ryabinin       2015-10-19  174  	case 1: *(__u8 *)res = *(volatile __u8 *)p; break;		\
d976441f Andrey Ryabinin       2015-10-19  175  	case 2: *(__u16 *)res = *(volatile __u16 *)p; break;		\
d976441f Andrey Ryabinin       2015-10-19  176  	case 4: *(__u32 *)res = *(volatile __u32 *)p; break;		\
d976441f Andrey Ryabinin       2015-10-19 @177  	case 8: *(__u64 *)res = *(volatile __u64 *)p; break;		\
d976441f Andrey Ryabinin       2015-10-19  178  	default:							\
d976441f Andrey Ryabinin       2015-10-19  179  		barrier();						\
d976441f Andrey Ryabinin       2015-10-19  180  		__builtin_memcpy((void *)res, (const void *)p, size);	\
d976441f Andrey Ryabinin       2015-10-19  181  		barrier();						\
d976441f Andrey Ryabinin       2015-10-19  182  	}								\
d976441f Andrey Ryabinin       2015-10-19  183  })
d976441f Andrey Ryabinin       2015-10-19  184  

:::::: The code at line 177 was first introduced by commit
:::::: d976441f44bc5d48635d081d277aa76556ffbf8b compiler, atomics, kasan: Provide READ_ONCE_NOCHECK()

:::::: TO: Andrey Ryabinin <aryabinin@...tuozzo.com>
:::::: CC: Ingo Molnar <mingo@...nel.org>

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