tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   01c8787d7f7ea56c16d94cf7133022189be231ad
commit: 68c3a763cd182bbfdcb4bdd4561776c87158a6cc [2067/2223] mm: add tracepoint for scanning pages
config: x86_64-randconfig-h0-09171202 (attached as .config)
reproduce:
  git checkout 68c3a763cd182bbfdcb4bdd4561776c87158a6cc
  # 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 include/trace/events/huge_memory.h:7:0,
                    from mm/huge_memory.c:59:
   mm/huge_memory.c: In function 'khugepaged':
>> include/linux/tracepoint.h:141:5: warning: 'isolated' may be used uninitialized in this function [-Wmaybe-uninitialized]
        ((void(*)(proto))(it_func))(args); \
        ^
   mm/huge_memory.c:2567:6: note: 'isolated' was declared here
     int isolated, result = 0;
         ^

vim +/isolated +141 include/linux/tracepoint.h

97e1c18e Mathieu Desnoyers 2008-07-18  125   */
2fbb90db Steven Rostedt    2012-02-07  126  #define __DO_TRACE(tp, proto, args, cond, prercu, postrcu)		\
97e1c18e Mathieu Desnoyers 2008-07-18  127  	do {								\
38516ab5 Steven Rostedt    2010-04-20  128  		struct tracepoint_func *it_func_ptr;			\
38516ab5 Steven Rostedt    2010-04-20  129  		void *it_func;						\
38516ab5 Steven Rostedt    2010-04-20  130  		void *__data;						\
97e1c18e Mathieu Desnoyers 2008-07-18  131  									\
287050d3 Steven Rostedt    2010-12-02  132  		if (!(cond))						\
287050d3 Steven Rostedt    2010-12-02  133  			return;						\
2fbb90db Steven Rostedt    2012-02-07  134  		prercu;							\
da7b3eab Mathieu Desnoyers 2008-11-14  135  		rcu_read_lock_sched_notrace();				\
38516ab5 Steven Rostedt    2010-04-20  136  		it_func_ptr = rcu_dereference_sched((tp)->funcs);	\
38516ab5 Steven Rostedt    2010-04-20  137  		if (it_func_ptr) {					\
97e1c18e Mathieu Desnoyers 2008-07-18  138  			do {						\
38516ab5 Steven Rostedt    2010-04-20  139  				it_func = (it_func_ptr)->func;		\
38516ab5 Steven Rostedt    2010-04-20  140  				__data = (it_func_ptr)->data;		\
38516ab5 Steven Rostedt    2010-04-20 @141  				((void(*)(proto))(it_func))(args);	\
38516ab5 Steven Rostedt    2010-04-20  142  			} while ((++it_func_ptr)->func);		\
97e1c18e Mathieu Desnoyers 2008-07-18  143  		}							\
da7b3eab Mathieu Desnoyers 2008-11-14  144  		rcu_read_unlock_sched_notrace();			\
2fbb90db Steven Rostedt    2012-02-07  145  		postrcu;						\
97e1c18e Mathieu Desnoyers 2008-07-18  146  	} while (0)
97e1c18e Mathieu Desnoyers 2008-07-18  147  
7ece55a4 Josh Triplett     2012-09-04  148  #ifndef MODULE
7ece55a4 Josh Triplett     2012-09-04  149  #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)	\

:::::: The code at line 141 was first introduced by commit
:::::: 38516ab59fbc5b3bb278cf5e1fe2867c70cff32e tracing: Let tracepoints have data passed to tracepoint callbacks

:::::: TO: Steven Rostedt <srostedt@redhat.com>
:::::: CC: Steven Rostedt <rostedt@goodmis.org>

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