Re: [PATCH 2/2] x86/idle: use dynamic halt poll

[kbuild test robot]

Hi Yang,

[auto build test WARNING on linus/master]
[also build test WARNING on v4.12-rc6]
[cannot apply to tip/x86/core next-20170622]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/root/x86-idle-add-halt-poll-for-halt-idle/20170623-061318
config: i386-randconfig-x016-06222129 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
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 >>):

   In file included from arch/x86/include/asm/preempt.h:5:0,
                    from include/linux/preempt.h:80,
                    from include/linux/spinlock.h:50,
                    from include/linux/mmzone.h:7,
                    from include/linux/gfp.h:5,
                    from include/linux/mm.h:9,
                    from arch/x86/kernel/process.c:5:
   arch/x86/kernel/process.c: In function 'check_poll':
>> arch/x86/include/asm/percpu.h:109:3: warning: 'val' may be used uninitialized in this function [-Wmaybe-uninitialized]
      asm(op "l %1,"__percpu_arg(0)  \
      ^~~
   arch/x86/kernel/process.c:351:15: note: 'val' was declared here
     unsigned int val, poll_duration;
                  ^~~
--
   In file included from arch/x86/include/asm/preempt.h:5:0,
                    from include/linux/preempt.h:80,
                    from include/linux/spinlock.h:50,
                    from include/linux/mmzone.h:7,
                    from include/linux/gfp.h:5,
                    from include/linux/mm.h:9,
                    from arch/x86//kernel/process.c:5:
   arch/x86//kernel/process.c: In function 'check_poll':
>> arch/x86/include/asm/percpu.h:109:3: warning: 'val' may be used uninitialized in this function [-Wmaybe-uninitialized]
      asm(op "l %1,"__percpu_arg(0)  \
      ^~~
   arch/x86//kernel/process.c:351:15: note: 'val' was declared here
     unsigned int val, poll_duration;
                  ^~~

vim +/val +109 arch/x86/include/asm/percpu.h

0f5e4816 arch/x86/include/asm/percpu.h Tejun Heo      2009-10-29   93  		pto_T__ pto_tmp__;			\
0f5e4816 arch/x86/include/asm/percpu.h Tejun Heo      2009-10-29   94  		pto_tmp__ = (val);			\
23b764d0 arch/x86/include/asm/percpu.h Andi Kleen     2010-06-10   95  		(void)pto_tmp__;			\
bc9e3be2 include/asm-x86/percpu.h      Joe Perches    2008-03-23   96  	}						\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30   97  	switch (sizeof(var)) {				\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30   98  	case 1:						\
87b26406 arch/x86/include/asm/percpu.h Brian Gerst    2009-01-19   99  		asm(op "b %1,"__percpu_arg(0)		\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  100  		    : "+m" (var)			\
0f5e4816 arch/x86/include/asm/percpu.h Tejun Heo      2009-10-29  101  		    : "qi" ((pto_T__)(val)));		\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  102  		break;					\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  103  	case 2:						\
87b26406 arch/x86/include/asm/percpu.h Brian Gerst    2009-01-19  104  		asm(op "w %1,"__percpu_arg(0)		\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  105  		    : "+m" (var)			\
0f5e4816 arch/x86/include/asm/percpu.h Tejun Heo      2009-10-29  106  		    : "ri" ((pto_T__)(val)));		\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  107  		break;					\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  108  	case 4:						\
87b26406 arch/x86/include/asm/percpu.h Brian Gerst    2009-01-19 @109  		asm(op "l %1,"__percpu_arg(0)		\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  110  		    : "+m" (var)			\
0f5e4816 arch/x86/include/asm/percpu.h Tejun Heo      2009-10-29  111  		    : "ri" ((pto_T__)(val)));		\
3334052a include/asm-x86/percpu.h      travis@xxxxxxx 2008-01-30  112  		break;					\
9939ddaf arch/x86/include/asm/percpu.h Tejun Heo      2009-01-13  113  	case 8:						\
87b26406 arch/x86/include/asm/percpu.h Brian Gerst    2009-01-19  114  		asm(op "q %1,"__percpu_arg(0)		\
9939ddaf arch/x86/include/asm/percpu.h Tejun Heo      2009-01-13  115  		    : "+m" (var)			\
0f5e4816 arch/x86/include/asm/percpu.h Tejun Heo      2009-10-29  116  		    : "re" ((pto_T__)(val)));		\
9939ddaf arch/x86/include/asm/percpu.h Tejun Heo      2009-01-13  117  		break;					\

:::::: The code at line 109 was first introduced by commit
:::::: 87b264065880fa696c121dad8498a60524e0f6de x86-64: Use absolute displacements for per-cpu accesses.

:::::: TO: Brian Gerst <brgerst@xxxxxxxxx>
:::::: CC: Tejun Heo <tj@xxxxxxxxxx>

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