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Message-Id: <20251025032221.2905818-14-libaokun@huaweicloud.com>
Date: Sat, 25 Oct 2025 11:22:09 +0800
From: libaokun@...weicloud.com
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu,
adilger.kernel@...ger.ca,
jack@...e.cz,
linux-kernel@...r.kernel.org,
kernel@...kajraghav.com,
mcgrof@...nel.org,
linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org,
yi.zhang@...wei.com,
yangerkun@...wei.com,
chengzhihao1@...wei.com,
libaokun1@...wei.com,
libaokun@...weicloud.com
Subject: [PATCH 13/25] ext4: support large block size in ext4_mb_init_cache()
From: Baokun Li <libaokun1@...wei.com>
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@...wei.com>
Reviewed-by: Zhang Yi <yi.zhang@...wei.com>
---
fs/ext4/mballoc.c | 44 ++++++++++++++++++++------------------------
1 file changed, 20 insertions(+), 24 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index d42d768a705a..31f4c7d65eb4 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1329,26 +1329,25 @@ 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;
@@ -1365,27 +1364,24 @@ 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_P_TO_LBLK(inode, folio->index) / 2;
+ for (i = 0, group = first_group; i < groups_per_folio; i++, group++) {
if (group >= ngroups)
break;
@@ -1393,7 +1389,7 @@ 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.
@@ -1413,7 +1409,7 @@ 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])
@@ -1423,8 +1419,8 @@ 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_P_TO_LBLK(inode, folio->index);
+ for (i = 0; i < blocks_per_folio; i++) {
group = (first_block + i) >> 1;
if (group >= ngroups)
break;
@@ -1501,7 +1497,7 @@ 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);
--
2.46.1
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