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ext4: support large block size in ext4_mb_init_cache()

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Currently, ext4_mb_init_cache() 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.

Since we now have the folio, we know its exact size. This allows us to
convert {blocks, groups}_per_page to {blocks, groups}_per_folio, thus
supporting block sizes greater than page size.

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: <20251121090654.631996-14-libaokun@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li
2025-11-21 17:06:43 +08:00
committed by Theodore Ts'o
parent 3938fc29f8
commit 0ad55fa104
1 changed files with 20 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

44
fs/ext4/mballoc.c
View File

@@ -1346,26 +1346,25 @@ static void mb_regenerate_buddy(struct ext4_buddy *e4b)
* block bitmap and buddy information. The information are
* stored in the inode as
*
* { page }
* { folio }
* [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
*
*
* one block each for bitmap and buddy information.
* So for each group we take up 2 blocks. A page can
* contain blocks_per_page (PAGE_SIZE / blocksize) blocks.
* So it can have information regarding groups_per_page which
* is blocks_per_page/2
* So for each group we take up 2 blocks. A folio can
* contain blocks_per_folio (folio_size / blocksize) blocks.
* So it can have information regarding groups_per_folio which
* is blocks_per_folio/2
*
* Locking note: This routine takes the block group lock of all groups
* for this page; do not hold this lock when calling this routine!
* for this folio; do not hold this lock when calling this routine!
*/
static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
{
ext4_group_t ngroups;
unsigned int blocksize;
int blocks_per_page;
int groups_per_page;
int blocks_per_folio;
int groups_per_folio;
int err = 0;
int i;
ext4_group_t first_group, group;
@@ -1382,27 +1381,24 @@ static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
sb = inode->i_sb;
ngroups = ext4_get_groups_count(sb);
blocksize = i_blocksize(inode);
blocks_per_page = PAGE_SIZE / blocksize;
blocks_per_folio = folio_size(folio) / blocksize;
WARN_ON_ONCE(!blocks_per_folio);
groups_per_folio = DIV_ROUND_UP(blocks_per_folio, 2);
mb_debug(sb, "init folio %lu\n", folio->index);
groups_per_page = blocks_per_page >> 1;
if (groups_per_page == 0)
groups_per_page = 1;
/* allocate buffer_heads to read bitmaps */
if (groups_per_page > 1) {
i = sizeof(struct buffer_head *) * groups_per_page;
if (groups_per_folio > 1) {
i = sizeof(struct buffer_head *) * groups_per_folio;
bh = kzalloc(i, gfp);
if (bh == NULL)
return -ENOMEM;
} else
bh = &bhs;
first_group = folio->index * blocks_per_page / 2;
/* read all groups the folio covers into the cache */
for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
first_group = EXT4_PG_TO_LBLK(inode, folio->index) / 2;
for (i = 0, group = first_group; i < groups_per_folio; i++, group++) {
if (group >= ngroups)
break;
@@ -1410,7 +1406,7 @@ static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
if (!grinfo)
continue;
/*
* If page is uptodate then we came here after online resize
* If folio is uptodate then we came here after online resize
* which added some new uninitialized group info structs, so
* we must skip all initialized uptodate buddies on the folio,
* which may be currently in use by an allocating task.
@@ -1430,7 +1426,7 @@ static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
}
/* wait for I/O completion */
for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
for (i = 0, group = first_group; i < groups_per_folio; i++, group++) {
int err2;
if (!bh[i])
@@ -1440,8 +1436,8 @@ static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
err = err2;
}
first_block = folio->index * blocks_per_page;
for (i = 0; i < blocks_per_page; i++) {
first_block = EXT4_PG_TO_LBLK(inode, folio->index);
for (i = 0; i < blocks_per_folio; i++) {
group = (first_block + i) >> 1;
if (group >= ngroups)
break;
@@ -1518,7 +1514,7 @@ static int ext4_mb_init_cache(struct folio *folio, char *incore, gfp_t gfp)
out:
if (bh) {
for (i = 0; i < groups_per_page; i++)
for (i = 0; i < groups_per_folio; i++)
brelse(bh[i]);
if (bh != &bhs)
kfree(bh);