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Subject[kbusch:alignment-fixes 3/3] block/bio.c:1229:6: warning: variable 'i' is used uninitialized whenever 'if' condition is true
tree:   https://git.kernel.org/pub/scm/linux/kernel/git/kbusch/linux.git alignment-fixes
head: 9d1ebc4c688471ccd3bffa5e6b08a82a71431f7b
commit: 9d1ebc4c688471ccd3bffa5e6b08a82a71431f7b [3/3] block: fix leaking page ref on truncated direct io
config: x86_64-randconfig-a012 (https://download.01.org/0day-ci/archive/20220706/202207060806.4qoJVWlL-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 142aca7741d5b06207e87bf4880fbe308c8d6823)
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://git.kernel.org/pub/scm/linux/kernel/git/kbusch/linux.git/commit/?id=9d1ebc4c688471ccd3bffa5e6b08a82a71431f7b
git remote add kbusch https://git.kernel.org/pub/scm/linux/kernel/git/kbusch/linux.git
git fetch --no-tags kbusch alignment-fixes
git checkout 9d1ebc4c688471ccd3bffa5e6b08a82a71431f7b
# 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 <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> block/bio.c:1229:6: warning: variable 'i' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
if (unlikely(size <= 0)) {
^~~~~~~~~~~~~~~~~~~
include/linux/compiler.h:78:22: note: expanded from macro 'unlikely'
# define unlikely(x) __builtin_expect(!!(x), 0)
^~~~~~~~~~~~~~~~~~~~~~~~~~
block/bio.c:1251:9: note: uninitialized use occurs here
while (i < nr_pages)
^
block/bio.c:1229:2: note: remove the 'if' if its condition is always false
if (unlikely(size <= 0)) {
^~~~~~~~~~~~~~~~~~~~~~~~~~
block/bio.c:1202:17: note: initialize the variable 'i' to silence this warning
unsigned len, i;
^
= 0
1 warning generated.


vim +1229 block/bio.c

1184
1185 /**
1186 * __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
1187 * @bio: bio to add pages to
1188 * @iter: iov iterator describing the region to be mapped
1189 *
1190 * Pins pages from *iter and appends them to @bio's bvec array. The
1191 * pages will have to be released using put_page() when done.
1192 * For multi-segment *iter, this function only adds pages from the
1193 * next non-empty segment of the iov iterator.
1194 */
1195 static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
1196 {
1197 unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
1198 unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
1199 struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
1200 struct page **pages = (struct page **)bv;
1201 ssize_t size, left;
1202 unsigned len, i;
1203 size_t offset;
1204 int ret = 0;
1205
1206 /*
1207 * Move page array up in the allocated memory for the bio vecs as far as
1208 * possible so that we can start filling biovecs from the beginning
1209 * without overwriting the temporary page array.
1210 */
1211 BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
1212 pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
1213
1214 /*
1215 * Each segment in the iov is required to be a block size multiple.
1216 * However, we may not be able to get the entire segment if it spans
1217 * more pages than bi_max_vecs allows, so we have to ALIGN_DOWN the
1218 * result to ensure the bio's total size is correct. The remainder of
1219 * the iov data will be picked up in the next bio iteration.
1220 */
1221 size = iov_iter_get_pages(iter, pages, UINT_MAX - bio->bi_iter.bi_size,
1222 nr_pages, &offset);
1223 if (size > 0) {
1224 nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE);
1225 size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));
1226 } else
1227 nr_pages = 0;
1228
> 1229 if (unlikely(size <= 0)) {
1230 ret = size ? size : -EFAULT;
1231 goto out;
1232 }
1233
1234 for (left = size, i = 0; left > 0; left -= len, i++) {
1235 struct page *page = pages[i];
1236
1237 len = min_t(size_t, PAGE_SIZE - offset, left);
1238 if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
1239 ret = bio_iov_add_zone_append_page(bio, page, len,
1240 offset);
1241 if (ret)
1242 break;
1243 } else
1244 bio_iov_add_page(bio, page, len, offset);
1245
1246 offset = 0;
1247 }
1248
1249 iov_iter_advance(iter, size - left);
1250 out:
1251 while (i < nr_pages)
1252 put_page(pages[i++]);
1253
1254 return ret;
1255 }
1256

--
0-DAY CI Kernel Test Service
https://01.org/lkp

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