Re: [PATCH v13 9/9] null_blk: add support for copy offload

[kernel test robot <lkp@intel.com>]

Hi Nitesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 53cdf865f90ba922a854c65ed05b519f9d728424]

url:    https://github.com/intel-lab-lkp/linux/commits/Nitesh-Shetty/block-Introduce-queue-limits-for-copy-offload-support/20230628-163126
base:   53cdf865f90ba922a854c65ed05b519f9d728424
patch link:    https://lore.kernel.org/r/20230627183629.26571-10-nj.shetty%40samsung.com
patch subject: [PATCH v13 9/9] null_blk: add support for copy offload
config: i386-randconfig-i006-20230628 (https://download.01.org/0day-ci/archive/20230628/202306282001.ba1qWTf0-lkp@intel.com/config)
compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project.git 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
reproduce: (https://download.01.org/0day-ci/archive/20230628/202306282001.ba1qWTf0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202306282001.ba1qWTf0-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/block/null_blk/main.c:1295:2: warning: variable 'rem' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
           __rq_for_each_bio(bio, req) {
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/blk-mq.h:1012:6: note: expanded from macro '__rq_for_each_bio'
           if ((rq->bio))                  \
               ^~~~~~~~~
   drivers/block/null_blk/main.c:1300:15: note: uninitialized use occurs here
           if (WARN_ON(!rem))
                        ^~~
   include/asm-generic/bug.h:123:25: note: expanded from macro 'WARN_ON'
           int __ret_warn_on = !!(condition);                              \
                                  ^~~~~~~~~
   drivers/block/null_blk/main.c:1295:2: note: remove the 'if' if its condition is always true
           __rq_for_each_bio(bio, req) {
           ^
   include/linux/blk-mq.h:1012:2: note: expanded from macro '__rq_for_each_bio'
           if ((rq->bio))                  \
           ^
   drivers/block/null_blk/main.c:1287:12: note: initialize the variable 'rem' to silence this warning
           size_t rem, temp;
                     ^
                      = 0
   1 warning generated.


vim +1295 drivers/block/null_blk/main.c

  1281	
  1282	static inline int nullb_setup_copy_write(struct nullb *nullb,
  1283			struct request *req, bool is_fua)
  1284	{
  1285		sector_t sector_in, sector_out;
  1286		void *in, *out;
  1287		size_t rem, temp;
  1288		struct bio *bio;
  1289		unsigned long offset_in, offset_out;
  1290		struct nullb_page *t_page_in, *t_page_out;
  1291		int ret = -EIO;
  1292	
  1293		sector_out = blk_rq_pos(req);
  1294	
> 1295		__rq_for_each_bio(bio, req) {
  1296			sector_in = bio->bi_iter.bi_sector;
  1297			rem = bio->bi_iter.bi_size;
  1298		}
  1299	
  1300		if (WARN_ON(!rem))
  1301			return BLK_STS_NOTSUPP;
  1302	
  1303		spin_lock_irq(&nullb->lock);
  1304		while (rem > 0) {
  1305			temp = min_t(size_t, nullb->dev->blocksize, rem);
  1306			offset_in = (sector_in & SECTOR_MASK) << SECTOR_SHIFT;
  1307			offset_out = (sector_out & SECTOR_MASK) << SECTOR_SHIFT;
  1308	
  1309			if (null_cache_active(nullb) && !is_fua)
  1310				null_make_cache_space(nullb, PAGE_SIZE);
  1311	
  1312			t_page_in = null_lookup_page(nullb, sector_in, false,
  1313				!null_cache_active(nullb));
  1314			if (!t_page_in)
  1315				goto err;
  1316			t_page_out = null_insert_page(nullb, sector_out,
  1317				!null_cache_active(nullb) || is_fua);
  1318			if (!t_page_out)
  1319				goto err;
  1320	
  1321			in = kmap_local_page(t_page_in->page);
  1322			out = kmap_local_page(t_page_out->page);
  1323	
  1324			memcpy(out + offset_out, in + offset_in, temp);
  1325			kunmap_local(out);
  1326			kunmap_local(in);
  1327			__set_bit(sector_out & SECTOR_MASK, t_page_out->bitmap);
  1328	
  1329			if (is_fua)
  1330				null_free_sector(nullb, sector_out, true);
  1331	
  1332			rem -= temp;
  1333			sector_in += temp >> SECTOR_SHIFT;
  1334			sector_out += temp >> SECTOR_SHIFT;
  1335		}
  1336	
  1337		ret = 0;
  1338	err:
  1339		spin_unlock_irq(&nullb->lock);
  1340		return ret;
  1341	}
  1342	

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