Hi Kairui,

[FYI, it's a private test report for your RFC patch.]
[auto build test WARNING on linux/master]
[also build test WARNING on linus/master v5.9-rc4 next-20200908]
[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]

url:    https://github.com/0day-ci/linux/commits/Kairui-Song/Add-writing-support-to-vmcore-for-reusing-oldmem/20200909-155222
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git bcf876870b95592b52519ed4aafcf9d95999bc9c
config: mips-randconfig-r035-20200909 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 8893d0816ccdf8998d2e21b5430e9d6abe7ef465)
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
        # install mips cross compiling tool for clang build
        # apt-get install binutils-mips-linux-gnu
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=mips 

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

All warnings (new ones prefixed by >>):

>> fs/proc/vmcore.c:118:14: warning: comparison of distinct pointer types ('typeof (to_copy) *' (aka 'unsigned int *') and 'typeof (((1UL) << 14) - offset) *' (aka 'unsigned long *')) [-Wcompare-distinct-pointer-types]
                   nr_bytes = min(to_copy, PAGE_SIZE - offset);
                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/kernel.h:884:19: note: expanded from macro 'min'
   #define min(x, y)       __careful_cmp(x, y, <)
                           ^~~~~~~~~~~~~~~~~~~~~~
   include/linux/kernel.h:875:24: note: expanded from macro '__careful_cmp'
           __builtin_choose_expr(__safe_cmp(x, y), \
                                 ^~~~~~~~~~~~~~~~
   include/linux/kernel.h:865:4: note: expanded from macro '__safe_cmp'
                   (__typecheck(x, y) && __no_side_effects(x, y))
                    ^~~~~~~~~~~~~~~~~
   include/linux/kernel.h:851:29: note: expanded from macro '__typecheck'
                   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                              ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~
   1 warning generated.

# https://github.com/0day-ci/linux/commit/03450912209f6cc4521a2d3a83d1cc8f4b5a850e
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Kairui-Song/Add-writing-support-to-vmcore-for-reusing-oldmem/20200909-155222
git checkout 03450912209f6cc4521a2d3a83d1cc8f4b5a850e
vim +118 fs/proc/vmcore.c

   104	
   105	/* Reads a page from the oldmem device from given offset. */
   106	ssize_t read_from_oldmem(char *buf, size_t count,
   107				 u64 *ppos, int userbuf,
   108				 bool encrypted)
   109	{
   110		unsigned long pfn, offset;
   111		size_t nr_bytes, to_copy = count;
   112		ssize_t tmp;
   113	
   114		offset = (unsigned long)(*ppos & (PAGE_SIZE - 1));
   115		pfn = (unsigned long)(*ppos / PAGE_SIZE);
   116	
   117		while (to_copy) {
 > 118			nr_bytes = min(to_copy, PAGE_SIZE - offset);
   119	
   120			/* If pfn is not ram, return zeros for sparse dump files */
   121			if (pfn_is_ram(pfn) == 0) {
   122				memset(buf, 0, nr_bytes);
   123			} else {
   124				if (encrypted)
   125					tmp = copy_oldmem_page_encrypted(pfn, buf,
   126									 nr_bytes,
   127									 offset,
   128									 userbuf);
   129				else
   130					tmp = copy_oldmem_page(pfn, buf, nr_bytes,
   131							       offset, userbuf);
   132	
   133				if (tmp < 0)
   134					return tmp;
   135			}
   136			*ppos += nr_bytes;
   137			buf += nr_bytes;
   138			to_copy -= nr_bytes;
   139			++pfn;
   140			offset = 0;
   141		}
   142	
   143		return count;
   144	}
   145	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org