dm cache: fix truncation bug when copying a block to/from >2TB fast device

During demotion or promotion to a cache's >2TB fast device we must not
truncate the cache block's associated sector to 32bits.  The 32bit
temporary result of from_cblock() caused a 32bit multiplication when
calculating the sector of the fast device in issue_copy_real().

Use an intermediate 64bit type to store the 32bit from_cblock() to allow
for proper 64bit multiplication.

Here is an example of how this bug manifests on an ext4 filesystem:

 EXT4-fs error (device dm-0): ext4_mb_generate_buddy:756: group 17136, 32768 clusters in bitmap, 30688 in gd; block bitmap corrupt.
 JBD2: Spotted dirty metadata buffer (dev = dm-0, blocknr = 0). There's a risk of filesystem corruption in case of system crash.
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org

drivers/md/dm-cache-target.c

@@ -979,12 +979,13 @@ static void issue_copy_real(struct dm_cache_migration *mg)
 	int r;
 	struct dm_io_region o_region, c_region;
 	struct cache *cache = mg->cache;
+	sector_t cblock = from_cblock(mg->cblock);
 
 	o_region.bdev = cache->origin_dev->bdev;
 	o_region.count = cache->sectors_per_block;
 
 	c_region.bdev = cache->cache_dev->bdev;
-	c_region.sector = from_cblock(mg->cblock) * cache->sectors_per_block;
+	c_region.sector = cblock * cache->sectors_per_block;
 	c_region.count = cache->sectors_per_block;
 
 	if (mg->writeback || mg->demote) {