Hi Zhongkun,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Zhongkun-He/mm-add-new-syscall-pidfd_set_mempolicy/20221111-164156
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20221111084051.2121029-1-hezhongkun.hzk%40bytedance.com
patch subject: [PATCH v2] mm: add new syscall pidfd_set_mempolicy().
config: x86_64-randconfig-a014
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/da593185d0d1e8a20d1084142960f9ee46c5871b
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Zhongkun-He/mm-add-new-syscall-pidfd_set_mempolicy/20221111-164156
        git checkout da593185d0d1e8a20d1084142960f9ee46c5871b
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot [off-list ref]

All warnings (new ones prefixed by >>):

quoted

mm/mempolicy.c:325:6: warning: no previous prototype for function 'mpol_put_async' [-Wmissing-prototypes]

   void mpol_put_async(struct task_struct *task, struct mempolicy *p)
        ^
   mm/mempolicy.c:325:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void mpol_put_async(struct task_struct *task, struct mempolicy *p)
   ^
   static 
   1 warning generated.


vim +/mpol_put_async +325 mm/mempolicy.c

   320	
   321	/*
   322	 * mpol destructor for pidfd_set_mempolicy().
   323	 * free mempolicy directly if task is null or task_work_add() failed.
   324	 */
 > 325	void mpol_put_async(struct task_struct *task, struct mempolicy *p)
   326	{
   327		enum task_work_notify_mode notify = TWA_RESUME;
   328	
   329		if (!atomic_dec_and_test(&p->refcnt))
   330			return;
   331	
   332		if (!task)
   333			goto out;
   334	
   335		init_task_work(&p->w.cb_head, mpol_free_async);
   336		if (task_work_pending(task))
   337			notify = TWA_SIGNAL; /* free memory in time */
   338	
   339		if (!task_work_add(task, &p->w.cb_head, notify))
   340			return;
   341	out:
   342		kmem_cache_free(policy_cache, p);
   343	}
   344	

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