Re: Question on smp_mb__before_spinlock

[kbuild test robot]

Hi Peter,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.8-rc5 next-20160825]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
[Suggest to use git(>=2.9.0) format-patch --base=<commit> (or --base=auto for convenience) to record what (public, well-known) commit your patch series was built on]
[Check https://git-scm.com/docs/git-format-patch for more information]

url:    https://github.com/0day-ci/linux/commits/Peter-Zijlstra/Question-on-smp_mb__before_spinlock/20160905-174026
config: x86_64-randconfig-x013-201636 (attached as .config)
compiler: gcc-6 (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   In file included from include/linux/sched.h:27:0,
                    from include/linux/kasan.h:4,
                    from include/linux/slab.h:118,
                    from include/linux/crypto.h:24,
                    from arch/x86/kernel/asm-offsets.c:8:
   include/linux/mm_types.h: In function 'set_tlb_flush_pending':
>> include/linux/mm_types.h:557:2: error: implicit declaration of function 'smp_mb__before_spinlock' [-Werror=implicit-function-declaration]
     smp_mb__before_spinlock();
     ^~~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors
   make[2]: *** [arch/x86/kernel/asm-offsets.s] Error 1
   make[2]: Target '__build' not remade because of errors.
   make[1]: *** [prepare0] Error 2
   make[1]: Target 'prepare' not remade because of errors.
   make: *** [sub-make] Error 2

vim +/smp_mb__before_spinlock +557 include/linux/mm_types.h

20841405 Rik van Riel 2013-12-18  551  	mm->tlb_flush_pending = true;
af2c1401 Mel Gorman   2013-12-18  552  
af2c1401 Mel Gorman   2013-12-18  553  	/*
af2c1401 Mel Gorman   2013-12-18  554  	 * Guarantee that the tlb_flush_pending store does not leak into the
af2c1401 Mel Gorman   2013-12-18  555  	 * critical section updating the page tables
af2c1401 Mel Gorman   2013-12-18  556  	 */
af2c1401 Mel Gorman   2013-12-18 @557  	smp_mb__before_spinlock();
20841405 Rik van Riel 2013-12-18  558  }
20841405 Rik van Riel 2013-12-18  559  /* Clearing is done after a TLB flush, which also provides a barrier. */
20841405 Rik van Riel 2013-12-18  560  static inline void clear_tlb_flush_pending(struct mm_struct *mm)

:::::: The code at line 557 was first introduced by commit
:::::: af2c1401e6f9177483be4fad876d0073669df9df mm: numa: guarantee that tlb_flush_pending updates are visible before page table updates

:::::: TO: Mel Gorman <mgorman@xxxxxxx>
:::::: CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

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