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ext4: support large block size in ext4_mb_load_buddy_gfp()

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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: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251121090654.631996-12-libaokun@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li
2025-11-21 17:06:41 +08:00
committed by Theodore Ts'o
parent 2a8de76b2b
commit 6117f1806a
1 changed files with 16 additions and 11 deletions
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27
fs/ext4/mballoc.c
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@@ -1659,17 +1659,15 @@ err:
/*
* 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;