[PATCH 6.18 248/752] ext4: move ext4_percpu_param_init() before ext4_mb_init()

Sasha Levin
2026-02-28T17:51:37Z

From: Baokun Li <libaokun1@huawei.com>

[ Upstream commit 270564513489d98b721a1e4a10017978d5213bff ]

When running `kvm-xfstests -c ext4/1k -C 1 generic/383` with the
`DOUBLE_CHECK` macro defined, the following panic is triggered:

==================================================================
EXT4-fs error (device vdc): ext4_validate_block_bitmap:423:
comm mount: bg 0: bad block bitmap checksum
BUG: unable to handle page fault for address: ff110000fa2cc000
PGD 3e01067 P4D 3e02067 PUD 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W
6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none)
RIP: 0010:percpu_counter_add_batch+0x13/0xa0
Call Trace:
<TASK>
ext4_mark_group_bitmap_corrupted+0xcb/0xe0
ext4_validate_block_bitmap+0x2a1/0x2f0
ext4_read_block_bitmap+0x33/0x50
mb_group_bb_bitmap_alloc+0x33/0x80
ext4_mb_add_groupinfo+0x190/0x250
ext4_mb_init_backend+0x87/0x290
ext4_mb_init+0x456/0x640
__ext4_fill_super+0x1072/0x1680
ext4_fill_super+0xd3/0x280
get_tree_bdev_flags+0x132/0x1d0
vfs_get_tree+0x29/0xd0
vfs_cmd_create+0x59/0xe0
__do_sys_fsconfig+0x4f6/0x6b0
do_syscall_64+0x50/0x1f0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
==================================================================

This issue can be reproduced using the following commands:
mkfs.ext4 -F -q -b 1024 /dev/sda 5G
tune2fs -O quota,project /dev/sda
mount /dev/sda /tmp/test

With DOUBLE_CHECK defined, mb_group_bb_bitmap_alloc() reads
and validates the block bitmap. When the validation fails,
ext4_mark_group_bitmap_corrupted() attempts to update
sbi->s_freeclusters_counter. However, this percpu_counter has not been
initialized yet at this point, which leads to the panic described above.

Fix this by moving the execution of ext4_percpu_param_init() to occur
before ext4_mb_init(), ensuring the per-CPU counters are initialized
before they are used.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20251209133116.731350-1-libaokun@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/super.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4ef5590c73fda..b5774f4101045 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5565,6 +5565,10 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
clear_opt2(sb, MB_OPTIMIZE_SCAN);
}

+ err = ext4_percpu_param_init(sbi);
+ if (err)
+ goto failed_mount5;
+
err = ext4_mb_init(sb);
if (err) {
ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
@@ -5580,10 +5584,6 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
sbi->s_journal->j_commit_callback =
ext4_journal_commit_callback;

- err = ext4_percpu_param_init(sbi);
- if (err)
- goto failed_mount6;
-
if (ext4_has_feature_flex_bg(sb))
if (!ext4_fill_flex_info(sb)) {
ext4_msg(sb, KERN_ERR,
@@ -5665,8 +5665,8 @@ failed_mount8: __maybe_unused
failed_mount6:
ext4_mb_release(sb);
ext4_flex_groups_free(sbi);
- ext4_percpu_param_destroy(sbi);
failed_mount5:
+ ext4_percpu_param_destroy(sbi);
ext4_ext_release(sb);
ext4_release_system_zone(sb);
failed_mount4a:
--
2.51.0