Hi David, I love your patch! Perhaps something to improve: [auto build test WARNING on debe436e77c72fcee804fb867f275e6d31aa999c] url: https://github.com/0day-ci/linux/commits/David-Hildenbrand/proc-vmcore-fi... base: debe436e77c72fcee804fb867f275e6d31aa999c config: i386-randconfig-s001-20211115 (https://download.01.org/0day-ci/archive/20211125/202111251406.V4R8NmsN-lk...) compiler: gcc-9 (Debian 9.3.0-22) 9.3.0 reproduce: # apt-get install sparse # sparse version: v0.6.4-dirty # https://github.com/0day-ci/linux/commit/c20846d5e7db81244d84acaab61b47462... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review David-Hildenbrand/proc-vmcore-fix-clearing-user-buffer-by-properly-using-clear_user/20211112-172947 git checkout c20846d5e7db81244d84acaab61b47462aaa8d13 # save the config file to linux build tree make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=i386 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; sparse warnings: (new ones prefixed by >>) fs/proc/vmcore.c:161:45: sparse: expected void [noderef] __user *mem fs/proc/vmcore.c:161:45: sparse: got char *buf vim +161 fs/proc/vmcore.c 133 134 /* Reads a page from the oldmem device from given offset. */ 135 ssize_t read_from_oldmem(char *buf, size_t count, 136 u64 *ppos, int userbuf, 137 bool encrypted) 138 { 139 unsigned long pfn, offset; 140 size_t nr_bytes; 141 ssize_t read = 0, tmp; 142 143 if (!count) 144 return 0; 145 146 offset = (unsigned long)(*ppos % PAGE_SIZE); 147 pfn = (unsigned long)(*ppos / PAGE_SIZE); 148 149 down_read(&vmcore_cb_rwsem); 150 do { 151 if (count > (PAGE_SIZE - offset)) 152 nr_bytes = PAGE_SIZE - offset; 153 else 154 nr_bytes = count; 155 156 /* If pfn is not ram, return zeros for sparse dump files */ 157 if (!pfn_is_ram(pfn)) { 158 tmp = 0; 159 if (!userbuf) 160 memset(buf, 0, nr_bytes); 162 tmp = -EFAULT; 163 } else { 164 if (encrypted) 165 tmp = copy_oldmem_page_encrypted(pfn, buf, 166 nr_bytes, 167 offset, 168 userbuf); 169 else 170 tmp = copy_oldmem_page(pfn, buf, nr_bytes, 171 offset, userbuf); 172 } 173 if (tmp < 0) { 174 up_read(&vmcore_cb_rwsem); 175 return tmp; 176 } 177 178 *ppos += nr_bytes; 179 count -= nr_bytes; 180 buf += nr_bytes; 181 read += nr_bytes; 182 ++pfn; 183 offset = 0; 184 } while (count); 185 186 up_read(&vmcore_cb_rwsem); 187 return read; 188 } 189 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org