Commit 6117f180 authored by Baokun Li's avatar Baokun Li Committed by Theodore Ts'o
Browse files

ext4: support large block size in ext4_mb_load_buddy_gfp() 



Currently, ext4_mb_load_buddy_gfp() uses blocks_per_page to calculate the
folio index and offset. However, when blocksize is larger than PAGE_SIZE,
blocks_per_page becomes zero, leading to a potential division-by-zero bug.

To support BS > PS, use bytes to compute folio index and offset within
folio to get rid of blocks_per_page.

Also, if buddy and bitmap land in the same folio, we get that folio’s ref
instead of looking it up again before updating the buddy.

Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Reviewed-by: default avatarZhang Yi <yi.zhang@huawei.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarOjaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251121090654.631996-12-libaokun@huaweicloud.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 2a8de76b

fs/ext4/mballoc.c

+16 −11
Original line number Diff line number Diff line
@@ -1659,17 +1659,15 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group, gfp_t gfp) 


/*

 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the

 * block group lock of all groups for this page; do not hold the BG lock when

 * block group lock of all groups for this folio; do not hold the BG lock when

 * calling this routine!

 */

static noinline_for_stack int

ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group,

		       struct ext4_buddy *e4b, gfp_t gfp)

{

	int blocks_per_page;

	int block;

	int pnum;

	int poff;

	struct folio *folio;

	int ret;

	struct ext4_group_info *grp;
@@ -1679,7 +1677,6 @@ ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group, 
	might_sleep();

	mb_debug(sb, "load group %u\n", group);



	blocks_per_page = PAGE_SIZE / sb->s_blocksize;

	grp = ext4_get_group_info(sb, group);

	if (!grp)

		return -EFSCORRUPTED;
@@ -1707,8 +1704,7 @@ ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group, 
	 * So for each group we need two blocks.

	 */

	block = group * 2;

	pnum = block / blocks_per_page;

	poff = block % blocks_per_page;

	pnum = EXT4_LBLK_TO_PG(inode, block);



	/* Avoid locking the folio in the fast path ... */

	folio = __filemap_get_folio(inode->i_mapping, pnum, FGP_ACCESSED, 0);
@@ -1740,7 +1736,8 @@ ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group, 
					goto err;

				}

				mb_cmp_bitmaps(e4b, folio_address(folio) +

					       (poff * sb->s_blocksize));

					offset_in_folio(folio,

						EXT4_LBLK_TO_B(inode, block)));

			}

			folio_unlock(folio);

		}
@@ -1756,12 +1753,18 @@ ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group, 


	/* Folios marked accessed already */

	e4b->bd_bitmap_folio = folio;

	e4b->bd_bitmap = folio_address(folio) + (poff * sb->s_blocksize);

	e4b->bd_bitmap = folio_address(folio) +

			 offset_in_folio(folio, EXT4_LBLK_TO_B(inode, block));



	block++;

	pnum = block / blocks_per_page;

	poff = block % blocks_per_page;

	pnum = EXT4_LBLK_TO_PG(inode, block);

	/* buddy and bitmap are on the same folio? */

	if (folio_contains(folio, pnum)) {

		folio_get(folio);

		goto update_buddy;

	}



	/* we need another folio for the buddy */

	folio = __filemap_get_folio(inode->i_mapping, pnum, FGP_ACCESSED, 0);

	if (IS_ERR(folio) || !folio_test_uptodate(folio)) {

		if (!IS_ERR(folio))
@@ -1796,9 +1799,11 @@ ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group, 
		goto err;

	}



update_buddy:

	/* Folios marked accessed already */

	e4b->bd_buddy_folio = folio;

	e4b->bd_buddy = folio_address(folio) + (poff * sb->s_blocksize);

	e4b->bd_buddy = folio_address(folio) +

			offset_in_folio(folio, EXT4_LBLK_TO_B(inode, block));



	return 0;