tree:   git://git.cmpxchg.org/linux-mmotm.git master
head:   6102e3c755ac0084fdce65f69a7a149fc51a8a86
commit: e45104f079e548146ac52b54e21d25668e7310ac [263/321] parse_integer: convert mm/
config: x86_64-rhel (attached as .config)
reproduce:
  git checkout e45104f079e548146ac52b54e21d25668e7310ac
  # 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 mm/memcontrol.c:64:0:
   mm/memcontrol.c: In function 'memcg_write_event_control':
>> include/linux/file.h:55:9: warning: 'cfd' may be used uninitialized in this function [-Wmaybe-uninitialized]
     return __to_fd(__fdget(fd));
            ^
   mm/memcontrol.c:3899:20: note: 'cfd' was declared here
     unsigned int efd, cfd;
                       ^

vim +/cfd +55 include/linux/file.h

a5b470ba Al Viro         2012-08-27  39  		fput(fd.file);
a5b470ba Al Viro         2012-08-27  40  }
a5b470ba Al Viro         2012-08-27  41  
b3c97528 Harvey Harrison 2008-02-13  42  extern struct file *fget(unsigned int fd);
bd2a31d5 Al Viro         2014-03-04  43  extern struct file *fget_raw(unsigned int fd);
bd2a31d5 Al Viro         2014-03-04  44  extern unsigned long __fdget(unsigned int fd);
bd2a31d5 Al Viro         2014-03-04  45  extern unsigned long __fdget_raw(unsigned int fd);
bd2a31d5 Al Viro         2014-03-04  46  extern unsigned long __fdget_pos(unsigned int fd);
a5b470ba Al Viro         2012-08-27  47  
bd2a31d5 Al Viro         2014-03-04  48  static inline struct fd __to_fd(unsigned long v)
a5b470ba Al Viro         2012-08-27  49  {
bd2a31d5 Al Viro         2014-03-04  50  	return (struct fd){(struct file *)(v & ~3),v & 3};
a5b470ba Al Viro         2012-08-27  51  }
a5b470ba Al Viro         2012-08-27  52  
bd2a31d5 Al Viro         2014-03-04  53  static inline struct fd fdget(unsigned int fd)
bd2a31d5 Al Viro         2014-03-04  54  {
bd2a31d5 Al Viro         2014-03-04 @55  	return __to_fd(__fdget(fd));
bd2a31d5 Al Viro         2014-03-04  56  }
2903ff01 Al Viro         2012-08-28  57  
a5b470ba Al Viro         2012-08-27  58  static inline struct fd fdget_raw(unsigned int fd)
a5b470ba Al Viro         2012-08-27  59  {
bd2a31d5 Al Viro         2014-03-04  60  	return __to_fd(__fdget_raw(fd));
a5b470ba Al Viro         2012-08-27  61  }
a5b470ba Al Viro         2012-08-27  62  
fe17f22d Al Viro         2012-08-21  63  extern int f_dupfd(unsigned int from, struct file *file, unsigned flags);

:::::: The code at line 55 was first introduced by commit
:::::: bd2a31d522344b3ac2fb680bd2366e77a9bd8209 get rid of fget_light()

:::::: TO: Al Viro <viro@zeniv.linux.org.uk>
:::::: CC: Al Viro <viro@zeniv.linux.org.uk>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation