Hi Gao,

[auto build test WARNING on nf-next/master]

url:    https://github.com/0day-ci/linux/commits/Pablo-Neira-Ayuso/netfilter-nf_ct_helper-define-pr_fmt/20160104-195139
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf-next master
config: i386-randconfig-x008-01040616 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

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 >>):

   net/netfilter/nf_conntrack_helper.c: In function 'nf_conntrack_helpers_register':
>> net/netfilter/nf_conntrack_helper.c:493:6: warning: 'err' may be used uninitialized in this function [-Wmaybe-uninitialized]
     int err;
         ^

vim +/err +493 net/netfilter/nf_conntrack_helper.c

   477		helper->help			= help;
   478		helper->from_nlattr		= from_nlattr;
   479		helper->me			= module;
   480	
   481		if (spec_port == default_port)
   482			snprintf(helper->name, sizeof(helper->name), "%s", name);
   483		else
   484			snprintf(helper->name, sizeof(helper->name), "%s-%u", name,
   485				 spec_port);
   486	}
   487	EXPORT_SYMBOL_GPL(nf_ct_helper_init);
   488	
   489	int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
   490					  unsigned int n)
   491	{
   492		unsigned int i;
 > 493		int err;
   494	
   495		for (i = 0; i < n; i++) {
   496			err = nf_conntrack_helper_register(&helper[i]);
   497			if (err < 0)
   498				goto err;
   499		}
   500	
   501		return err;

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