Hi Toshiki,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.4-rc6]
[cannot apply to next-20191108]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Toshiki-Fukasawa/make-pfn-walker-support-ZONE_DEVICE/20191110-000508
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 0058b0a506e40d9a2c62015fe92eb64a44d78cd9
config: i386-defconfig (attached as .config)
compiler: gcc-7 (Debian 7.4.0-14) 7.4.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   fs/proc/page.c: In function 'kpage_common_read':
>> fs/proc/page.c:46:17: error: implicit declaration of function 'pfn_zone_device'; did you mean 'bus_find_device'? [-Werror=implicit-function-declaration]
      if (!ppage && pfn_zone_device(pfn)) {
                    ^~~~~~~~~~~~~~~
                    bus_find_device
   cc1: some warnings being treated as errors

vim +46 fs/proc/page.c

    25	
    26	/*
    27	 * This is general function to read various data on pages.
    28	 */
    29	static ssize_t kpage_common_read(struct file *file, char __user *buf,
    30			size_t count, loff_t *ppos, read_page_data_fn_t read_fn)
    31	{
    32		u64 __user *out = (u64 __user *)buf;
    33		struct page *ppage;
    34		unsigned long src = *ppos;
    35		unsigned long pfn;
    36		unsigned long valid_pages = 0;
    37		ssize_t ret = 0;
    38	
    39		pfn = src / KPMSIZE;
    40		count = min_t(size_t, count, (max_pfn * KPMSIZE) - src);
    41		if (src & KPMMASK || count & KPMMASK)
    42			return -EINVAL;
    43	
    44		while (count > 0) {
    45			ppage = pfn_to_online_page(pfn);
  > 46			if (!ppage && pfn_zone_device(pfn)) {
    47				/*
    48				 * Skip to read first few uninitialized pages on
    49				 * ZONE_DEVICE. And count valid pages starting
    50				 * with the pfn so that minimize the number of
    51				 * calls to nr_valid_pages_zone_device().
    52				 */
    53				if (!valid_pages)
    54					valid_pages = nr_valid_pages_zone_device(pfn);
    55				if (valid_pages) {
    56					ppage = pfn_to_page(pfn);
    57					valid_pages--;
    58				}
    59			} else if (valid_pages) {
    60				/* ZONE_DEVICE has been hot removed */
    61				valid_pages = 0;
    62			}
    63	
    64			if (put_user(read_fn(ppage), out)) {
    65				ret = -EFAULT;
    66				break;
    67			}
    68	
    69			pfn++;
    70			out++;
    71			count -= KPMSIZE;
    72	
    73			cond_resched();
    74		}
    75	
    76		*ppos += (char __user *)out - buf;
    77		if (!ret)
    78			ret = (char __user *)out - buf;
    79		return ret;
    80	}
    81	

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