Re: [PATCH v2] writeback: safer lock nesting

[kbuild test robot <lkp@intel.com>]

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Hi Greg,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.16]
[cannot apply to next-20180406]
[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/Greg-Thelen/writeback-safer-lock-nesting/20180407-122200
config: mips-db1xxx_defconfig (attached as .config)
compiler: mipsel-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=mips 

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/mips/include/asm/atomic.h:17:0,
                    from include/linux/atomic.h:5,
                    from arch/mips/include/asm/processor.h:14,
                    from arch/mips/include/asm/thread_info.h:16,
                    from include/linux/thread_info.h:38,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/mips/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:81,
                    from include/linux/spinlock.h:51,
                    from mm/page-writeback.c:16:
   mm/page-writeback.c: In function 'account_page_redirty':
>> include/linux/irqflags.h:80:3: warning: 'cookie.flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
      arch_local_irq_restore(flags);  \
      ^~~~~~~~~~~~~~~~~~~~~~
   mm/page-writeback.c:2504:25: note: 'cookie.flags' was declared here
      struct wb_lock_cookie cookie;
                            ^~~~~~
   In file included from arch/mips/include/asm/atomic.h:17:0,
                    from include/linux/atomic.h:5,
                    from arch/mips/include/asm/processor.h:14,
                    from arch/mips/include/asm/thread_info.h:16,
                    from include/linux/thread_info.h:38,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/mips/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:81,
                    from include/linux/spinlock.h:51,
                    from mm/page-writeback.c:16:
   mm/page-writeback.c: In function '__cancel_dirty_page':
>> include/linux/irqflags.h:80:3: warning: 'cookie.flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
      arch_local_irq_restore(flags);  \
      ^~~~~~~~~~~~~~~~~~~~~~
   mm/page-writeback.c:2616:25: note: 'cookie.flags' was declared here
      struct wb_lock_cookie cookie;
                            ^~~~~~
   In file included from arch/mips/include/asm/atomic.h:17:0,
                    from include/linux/atomic.h:5,
                    from arch/mips/include/asm/processor.h:14,
                    from arch/mips/include/asm/thread_info.h:16,
                    from include/linux/thread_info.h:38,
                    from include/asm-generic/preempt.h:5,
                    from ./arch/mips/include/generated/asm/preempt.h:1,
                    from include/linux/preempt.h:81,
                    from include/linux/spinlock.h:51,
                    from mm/page-writeback.c:16:
   mm/page-writeback.c: In function 'clear_page_dirty_for_io':
>> include/linux/irqflags.h:80:3: warning: 'cookie.flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
      arch_local_irq_restore(flags);  \
      ^~~~~~~~~~~~~~~~~~~~~~
   mm/page-writeback.c:2656:25: note: 'cookie.flags' was declared here
      struct wb_lock_cookie cookie;
                            ^~~~~~

vim +80 include/linux/irqflags.h

81d68a96 Steven Rostedt 2008-05-12  66  
df9ee292 David Howells  2010-10-07  67  /*
df9ee292 David Howells  2010-10-07  68   * Wrap the arch provided IRQ routines to provide appropriate checks.
df9ee292 David Howells  2010-10-07  69   */
df9ee292 David Howells  2010-10-07  70  #define raw_local_irq_disable()		arch_local_irq_disable()
df9ee292 David Howells  2010-10-07  71  #define raw_local_irq_enable()		arch_local_irq_enable()
df9ee292 David Howells  2010-10-07  72  #define raw_local_irq_save(flags)			\
df9ee292 David Howells  2010-10-07  73  	do {						\
df9ee292 David Howells  2010-10-07  74  		typecheck(unsigned long, flags);	\
df9ee292 David Howells  2010-10-07  75  		flags = arch_local_irq_save();		\
df9ee292 David Howells  2010-10-07  76  	} while (0)
df9ee292 David Howells  2010-10-07  77  #define raw_local_irq_restore(flags)			\
df9ee292 David Howells  2010-10-07  78  	do {						\
df9ee292 David Howells  2010-10-07  79  		typecheck(unsigned long, flags);	\
df9ee292 David Howells  2010-10-07 @80  		arch_local_irq_restore(flags);		\
df9ee292 David Howells  2010-10-07  81  	} while (0)
df9ee292 David Howells  2010-10-07  82  #define raw_local_save_flags(flags)			\
df9ee292 David Howells  2010-10-07  83  	do {						\
df9ee292 David Howells  2010-10-07  84  		typecheck(unsigned long, flags);	\
df9ee292 David Howells  2010-10-07  85  		flags = arch_local_save_flags();	\
df9ee292 David Howells  2010-10-07  86  	} while (0)
df9ee292 David Howells  2010-10-07  87  #define raw_irqs_disabled_flags(flags)			\
df9ee292 David Howells  2010-10-07  88  	({						\
df9ee292 David Howells  2010-10-07  89  		typecheck(unsigned long, flags);	\
df9ee292 David Howells  2010-10-07  90  		arch_irqs_disabled_flags(flags);	\
df9ee292 David Howells  2010-10-07  91  	})
df9ee292 David Howells  2010-10-07  92  #define raw_irqs_disabled()		(arch_irqs_disabled())
df9ee292 David Howells  2010-10-07  93  #define raw_safe_halt()			arch_safe_halt()
de30a2b3 Ingo Molnar    2006-07-03  94  

:::::: The code at line 80 was first introduced by commit
:::::: df9ee29270c11dba7d0fe0b83ce47a4d8e8d2101 Fix IRQ flag handling naming

:::::: TO: David Howells <dhowells@redhat.com>
:::::: CC: David Howells <dhowells@redhat.com>

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