Re: [PATCH] locking/osq_lock: Avoid false sharing in optimistic_spin_node

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

Hi Zeng,

kernel test robot noticed the following build errors:

[auto build test ERROR on tip/locking/core]
[also build test ERROR on linus/master v6.7-rc6 next-20231220]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Zeng-Heng/locking-osq_lock-Avoid-false-sharing-in-optimistic_spin_node/20231220-150010
base:   tip/locking/core
patch link:    https://lore.kernel.org/r/20231220070204.2662730-1-zengheng4%40huawei.com
patch subject: [PATCH] locking/osq_lock: Avoid false sharing in optimistic_spin_node
config: arm-defconfig (https://download.01.org/0day-ci/archive/20231221/202312210155.Wc2HUK8C-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project.git f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231221/202312210155.Wc2HUK8C-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202312210155.Wc2HUK8C-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from arch/arm/kernel/asm-offsets.c:11:
   In file included from include/linux/sched.h:15:
   In file included from include/linux/sem.h:5:
   In file included from include/uapi/linux/sem.h:5:
   In file included from include/linux/ipc.h:7:
   In file included from include/linux/rhashtable-types.h:14:
   In file included from include/linux/mutex.h:20:
>> include/linux/osq_lock.h:16:9: error: expected ';' at end of declaration list
           int cpu ____cacheline_aligned;
                  ^
                  ;
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:97:11: warning: array index 3 is past the end of the array (which contains 2 elements) [-Warray-bounds]
                   return (set->sig[3] | set->sig[2] |
                           ^        ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:97:25: warning: array index 2 is past the end of the array (which contains 2 elements) [-Warray-bounds]
                   return (set->sig[3] | set->sig[2] |
                                         ^        ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:113:11: warning: array index 3 is past the end of the array (which contains 2 elements) [-Warray-bounds]
                   return  (set1->sig[3] == set2->sig[3]) &&
                            ^         ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:113:27: warning: array index 3 is past the end of the array (which contains 2 elements) [-Warray-bounds]
                   return  (set1->sig[3] == set2->sig[3]) &&
                                            ^         ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:114:5: warning: array index 2 is past the end of the array (which contains 2 elements) [-Warray-bounds]
                           (set1->sig[2] == set2->sig[2]) &&
                            ^         ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:114:21: warning: array index 2 is past the end of the array (which contains 2 elements) [-Warray-bounds]
                           (set1->sig[2] == set2->sig[2]) &&
                                            ^         ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:
   In file included from include/linux/fs.h:33:
   In file included from include/linux/percpu-rwsem.h:7:
   In file included from include/linux/rcuwait.h:6:
   In file included from include/linux/sched/signal.h:6:
   include/linux/signal.h:156:1: warning: array index 3 is past the end of the array (which contains 2 elements) [-Warray-bounds]
   _SIG_SET_BINOP(sigorsets, _sig_or)
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/signal.h:137:8: note: expanded from macro '_SIG_SET_BINOP'
                   a3 = a->sig[3]; a2 = a->sig[2];                         \
                        ^      ~
   arch/arm/include/asm/signal.h:17:2: note: array 'sig' declared here
           unsigned long sig[_NSIG_WORDS];
           ^
   In file included from arch/arm/kernel/asm-offsets.c:12:
   In file included from include/linux/mm.h:1084:
   In file included from include/linux/huge_mm.h:8:


vim +16 include/linux/osq_lock.h

     4	
     5	/*
     6	 * An MCS like lock especially tailored for optimistic spinning for sleeping
     7	 * lock implementations (mutex, rwsem, etc).
     8	 */
     9	struct optimistic_spin_node {
    10		struct optimistic_spin_node *next, *prev;
    11		int locked; /* 1 if lock acquired */
    12		/*
    13		 * Stores an encoded CPU # + 1 value.
    14		 * Only read by other cpus, so split into different cache lines.
    15		 */
  > 16		int cpu ____cacheline_aligned;
    17	};
    18	

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