[openeuler:openEuler-1.0-LTS 13169/23386] mm/userfaultfd.o: warning: objtool: mcopy_atomic()+0x1e78: unreachable instruction

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

tree:   https://gitee.com/openeuler/kernel.git openEuler-1.0-LTS
head:   e5ea67ef45bf84add14bf009f071b29909f087cb
commit: 8b9ea9010139596e71aae4be5264c3dd901b13cb [13169/23386] pagecache: support percpu refcount to imporve performance
config: x86_64-randconfig-003-20240731 (https://download.01.org/0day-ci/archive/20240731/202407311035.uLDyyIFP-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240731/202407311035.uLDyyIFP-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/202407311035.uLDyyIFP-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from mm/userfaultfd.c:12:
   include/linux/pagemap.h:425:21: warning: cast from 'int (*)(struct file *, struct page *)' to 'filler_t *' (aka 'int (*)(void *, struct page *)') converts to incompatible function type [-Wcast-function-type-strict]
     425 |         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
         |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   1 warning generated.
>> mm/userfaultfd.o: warning: objtool: mcopy_atomic()+0x1e78: unreachable instruction

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