On Mar 30, 2021, at 6:59 PM, kernel test robot [off-list ref] wrote:

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   4143e05b7b171902f4938614c2a68821e1af46bc
commit: 254c271da0712ea8914f187588e0f81f7678ee2f [6117/8451] md/raid10: improve discard request for far layout
compiler: aarch64-linux-gcc (GCC) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>


cppcheck warnings: (new ones prefixed by >>)
  In file included from drivers/md/raid10.c:

quoted

quoted

drivers/md/raid10.c:1707:39: warning: Uninitialized variable: first_r10bio [uninitvar]

    r10_bio->master_bio = (struct bio *)first_r10bio;
                                        ^

vim +1707 drivers/md/raid10.c

 1573	
 1574	/*
 1575	 * There are some limitations to handle discard bio
 1576	 * 1st, the discard size is bigger than stripe_size*2.
 1577	 * 2st, if the discard bio spans reshape progress, we use the old way to
 1578	 * handle discard bio
 1579	 */
 1580	static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
 1581	{
 1582		struct r10conf *conf = mddev->private;
 1583		struct geom *geo = &conf->geo;
 1584		int far_copies = geo->far_copies;
 1585		bool first_copy = true;
 1586		struct r10bio *r10_bio, *first_r10bio;
 1587		struct bio *split;
 1588		int disk;
 1589		sector_t chunk;
 1590		unsigned int stripe_size;
 1591		unsigned int stripe_data_disks;
 1592		sector_t split_size;
 1593		sector_t bio_start, bio_end;
 1594		sector_t first_stripe_index, last_stripe_index;
 1595		sector_t start_disk_offset;
 1596		unsigned int start_disk_index;
 1597		sector_t end_disk_offset;
 1598		unsigned int end_disk_index;
 1599		unsigned int remainder;
 1600	
 1601		if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 1602			return -EAGAIN;
 1603	
 1604		wait_barrier(conf);
 1605	
 1606		/*
 1607		 * Check reshape again to avoid reshape happens after checking
 1608		 * MD_RECOVERY_RESHAPE and before wait_barrier
 1609		 */
 1610		if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
 1611			goto out;
 1612	
 1613		if (geo->near_copies)
 1614			stripe_data_disks = geo->raid_disks / geo->near_copies +
 1615						geo->raid_disks % geo->near_copies;
 1616		else
 1617			stripe_data_disks = geo->raid_disks;
 1618	
 1619		stripe_size = stripe_data_disks << geo->chunk_shift;
 1620	
 1621		bio_start = bio->bi_iter.bi_sector;
 1622		bio_end = bio_end_sector(bio);
 1623	
 1624		/*
 1625		 * Maybe one discard bio is smaller than strip size or across one
 1626		 * stripe and discard region is larger than one stripe size. For far
 1627		 * offset layout, if the discard region is not aligned with stripe
 1628		 * size, there is hole when we submit discard bio to member disk.
 1629		 * For simplicity, we only handle discard bio which discard region
 1630		 * is bigger than stripe_size * 2
 1631		 */
 1632		if (bio_sectors(bio) < stripe_size*2)
 1633			goto out;
 1634	
 1635		/*
 1636		 * Keep bio aligned with strip size.
 1637		 */
 1638		div_u64_rem(bio_start, stripe_size, &remainder);
 1639		if (remainder) {
 1640			split_size = stripe_size - remainder;
 1641			split = bio_split(bio, split_size, GFP_NOIO, &conf->bio_split);
 1642			bio_chain(split, bio);
 1643			allow_barrier(conf);
 1644			/* Resend the fist split part */
 1645			submit_bio_noacct(split);
 1646			wait_barrier(conf);
 1647		}
 1648		div_u64_rem(bio_end, stripe_size, &remainder);
 1649		if (remainder) {
 1650			split_size = bio_sectors(bio) - remainder;
 1651			split = bio_split(bio, split_size, GFP_NOIO, &conf->bio_split);
 1652			bio_chain(split, bio);
 1653			allow_barrier(conf);
 1654			/* Resend the second split part */
 1655			submit_bio_noacct(bio);
 1656			bio = split;
 1657			wait_barrier(conf);
 1658		}
 1659	
 1660		bio_start = bio->bi_iter.bi_sector;
 1661		bio_end = bio_end_sector(bio);
 1662	
 1663		/*
 1664		 * Raid10 uses chunk as the unit to store data. It's similar like raid0.
 1665		 * One stripe contains the chunks from all member disk (one chunk from
 1666		 * one disk at the same HBA address). For layout detail, see 'man md 4'
 1667		 */
 1668		chunk = bio_start >> geo->chunk_shift;
 1669		chunk *= geo->near_copies;
 1670		first_stripe_index = chunk;
 1671		start_disk_index = sector_div(first_stripe_index, geo->raid_disks);
 1672		if (geo->far_offset)
 1673			first_stripe_index *= geo->far_copies;
 1674		start_disk_offset = (bio_start & geo->chunk_mask) +
 1675					(first_stripe_index << geo->chunk_shift);
 1676	
 1677		chunk = bio_end >> geo->chunk_shift;
 1678		chunk *= geo->near_copies;
 1679		last_stripe_index = chunk;
 1680		end_disk_index = sector_div(last_stripe_index, geo->raid_disks);
 1681		if (geo->far_offset)
 1682			last_stripe_index *= geo->far_copies;
 1683		end_disk_offset = (bio_end & geo->chunk_mask) +
 1684					(last_stripe_index << geo->chunk_shift);
 1685	
 1686	retry_discard:
 1687		r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
 1688		r10_bio->mddev = mddev;
 1689		r10_bio->state = 0;
 1690		r10_bio->sectors = 0;
 1691		memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
 1692		wait_blocked_dev(mddev, r10_bio);
 1693	
 1694		/*
 1695		 * For far layout it needs more than one r10bio to cover all regions.
 1696		 * Inspired by raid10_sync_request, we can use the first r10bio->master_bio
 1697		 * to record the discard bio. Other r10bio->master_bio record the first
 1698		 * r10bio. The first r10bio only release after all other r10bios finish.
 1699		 * The discard bio returns only first r10bio finishes
 1700		 */
 1701		if (first_copy) {
 1702			r10_bio->master_bio = bio;
 1703			set_bit(R10BIO_Discard, &r10_bio->state);
 1704			first_copy = false;
 1705			first_r10bio = r10_bio;
 1706		} else

quoted

1707			r10_bio->master_bio = (struct bio *)first_r10bio;

This is a false alert. The function starts with first_copy = true. When we 
hit else clause, first_r10bio is already initialized. 

Thanks,
Song

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