[PATCH 5.15 244/245] ext4: avoid bb_free and bb_fragments inconsistency in mb_free_blocks()

Greg Kroah-Hartman
2024-02-27T14:12:28Z

From: Baokun Li <libaokun1@huawei.com>

commit 2331fd4a49864e1571b4f50aa3aa1536ed6220d0 upstream.

After updating bb_free in mb_free_blocks, it is possible to return without
updating bb_fragments because the block being freed is found to have
already been freed, which leads to inconsistency between bb_free and
bb_fragments.

Since the group may be unlocked in ext4_grp_locked_error(), this can lead
to problems such as dividing by zero when calculating the average fragment
length. Hence move the update of bb_free to after the block double-free
check guarantees that the corresponding statistics are updated only after
the core block bitmap is modified.

Fixes: eabe0444df90 ("ext4: speed-up releasing blocks on commit")
CC: <stable@vger.kernel.org> # 3.10
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240104142040.2835097-5-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/mballoc.c | 39 +++++++++++++++++++++------------------
1 file changed, 21 insertions(+), 18 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1835,11 +1835,6 @@ static void mb_free_blocks(struct inode
mb_check_buddy(e4b);
mb_free_blocks_double(inode, e4b, first, count);

- this_cpu_inc(discard_pa_seq);
- e4b->bd_info->bb_free += count;
- if (first < e4b->bd_info->bb_first_free)
- e4b->bd_info->bb_first_free = first;
-
/* access memory sequentially: check left neighbour,
* clear range and then check right neighbour
*/
@@ -1853,23 +1848,31 @@ static void mb_free_blocks(struct inode
struct ext4_sb_info *sbi = EXT4_SB(sb);
ext4_fsblk_t blocknr;

+ /*
+ * Fastcommit replay can free already freed blocks which
+ * corrupts allocation info. Regenerate it.
+ */
+ if (sbi->s_mount_state & EXT4_FC_REPLAY) {
+ mb_regenerate_buddy(e4b);
+ goto check;
+ }
+
blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
blocknr += EXT4_C2B(sbi, block);
- if (!(sbi->s_mount_state & EXT4_FC_REPLAY)) {
- ext4_grp_locked_error(sb, e4b->bd_group,
- inode ? inode->i_ino : 0,
- blocknr,
- "freeing already freed block (bit %u); block bitmap corrupt.",
- block);
- ext4_mark_group_bitmap_corrupted(
- sb, e4b->bd_group,
+ ext4_grp_locked_error(sb, e4b->bd_group,
+ inode ? inode->i_ino : 0, blocknr,
+ "freeing already freed block (bit %u); block bitmap corrupt.",
+ block);
+ ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
EXT4_GROUP_INFO_BBITMAP_CORRUPT);
- } else {
- mb_regenerate_buddy(e4b);
- }
- goto done;
+ return;
}

+ this_cpu_inc(discard_pa_seq);
+ e4b->bd_info->bb_free += count;
+ if (first < e4b->bd_info->bb_first_free)
+ e4b->bd_info->bb_first_free = first;
+
/* let's maintain fragments counter */
if (left_is_free && right_is_free)
e4b->bd_info->bb_fragments--;
@@ -1894,9 +1897,9 @@ static void mb_free_blocks(struct inode
if (first <= last)
mb_buddy_mark_free(e4b, first >> 1, last >> 1);

-done:
mb_set_largest_free_order(sb, e4b->bd_info);
mb_update_avg_fragment_size(sb, e4b->bd_info);
+check:
mb_check_buddy(e4b);
}