linux-kernel - Re: [PATCH] ext4: move ext4_percpu_param_init() before ext4_mb

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Message-ID: <odu3phjd54iv3zi7tft7ftmmn24hjgzszgd7456gh2cg2gbl4r@jgonvxf5ssfr>
Date: Wed, 10 Dec 2025 11:14:33 +0100
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, 
	jack@...e.cz, linux-kernel@...r.kernel.org, yi.zhang@...wei.com, 
	yangerkun@...wei.com, libaokun1@...wei.com
Subject: Re: [PATCH] ext4: move ext4_percpu_param_init() before ext4_mb_init()

On Tue 09-12-25 21:31:16, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> 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@...wei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  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 87205660c5d0..5c2e931d8a53 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5599,35 +5599,35 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  	 */
>  	if (!(ctx->spec & EXT4_SPEC_mb_optimize_scan)) {
>  		if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
>  			set_opt2(sb, MB_OPTIMIZE_SCAN);
>  		else
>  			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)",
>  			 err);
>  		goto failed_mount5;
>  	}
>  
>  	/*
>  	 * We can only set up the journal commit callback once
>  	 * mballoc is initialized
>  	 */
>  	if (sbi->s_journal)
>  		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,
>  			       "unable to initialize "
>  			       "flex_bg meta info!");
>  			err = -ENOMEM;
>  			goto failed_mount6;
>  		}
> @@ -5699,18 +5699,18 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  	ext4_quotas_off(sb, EXT4_MAXQUOTAS);
>  failed_mount8: __maybe_unused
>  	ext4_release_orphan_info(sb);
>  failed_mount7:
>  	ext4_unregister_li_request(sb);
>  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:
>  	dput(sb->s_root);
>  	sb->s_root = NULL;
>  failed_mount4:
>  	ext4_msg(sb, KERN_ERR, "mount failed");
>  	if (EXT4_SB(sb)->rsv_conversion_wq)
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR