linux-ext4 - Re: [PATCH v2 09/16] ext4: fix zombie groups in average fragment size lists

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <pouh5hfd7lswwhczu667k2pywuawaetvv4lr44zinexbb75jeu@rgaaqa5myop7>
Date: Fri, 27 Jun 2025 21:14:31 +0200
From: Jan Kara <jack@...e.cz>
To: Baokun Li <libaokun1@...wei.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz, 
	adilger.kernel@...ger.ca, ojaswin@...ux.ibm.com, linux-kernel@...r.kernel.org, 
	yi.zhang@...wei.com, yangerkun@...wei.com, stable@...r.kernel.org
Subject: Re: [PATCH v2 09/16] ext4: fix zombie groups in average fragment
 size lists

On Mon 23-06-25 15:32:57, Baokun Li wrote:
> Groups with no free blocks shouldn't be in any average fragment size list.
> However, when all blocks in a group are allocated(i.e., bb_fragments or
> bb_free is 0), we currently skip updating the average fragment size, which
> means the group isn't removed from its previous s_mb_avg_fragment_size[old]
> list.
> 
> This created "zombie" groups that were always skipped during traversal as
> they couldn't satisfy any block allocation requests, negatively impacting
> traversal efficiency.
> 
> Therefore, when a group becomes completely free, bb_avg_fragment_size_order
					     ^^^ full

> is now set to -1. If the old order was not -1, a removal operation is
> performed; if the new order is not -1, an insertion is performed.
> 
> Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning")
> CC: stable@...r.kernel.org
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

Good catch! The patch looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/mballoc.c | 36 ++++++++++++++++++------------------
>  1 file changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 94950b07a577..e6d6c2da3c6e 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -841,30 +841,30 @@ static void
>  mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
>  {
>  	struct ext4_sb_info *sbi = EXT4_SB(sb);
> -	int new_order;
> +	int new, old;
>  
> -	if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_fragments == 0)
> +	if (!test_opt2(sb, MB_OPTIMIZE_SCAN))
>  		return;
>  
> -	new_order = mb_avg_fragment_size_order(sb,
> -					grp->bb_free / grp->bb_fragments);
> -	if (new_order == grp->bb_avg_fragment_size_order)
> +	old = grp->bb_avg_fragment_size_order;
> +	new = grp->bb_fragments == 0 ? -1 :
> +	      mb_avg_fragment_size_order(sb, grp->bb_free / grp->bb_fragments);
> +	if (new == old)
>  		return;
>  
> -	if (grp->bb_avg_fragment_size_order != -1) {
> -		write_lock(&sbi->s_mb_avg_fragment_size_locks[
> -					grp->bb_avg_fragment_size_order]);
> +	if (old >= 0) {
> +		write_lock(&sbi->s_mb_avg_fragment_size_locks[old]);
>  		list_del(&grp->bb_avg_fragment_size_node);
> -		write_unlock(&sbi->s_mb_avg_fragment_size_locks[
> -					grp->bb_avg_fragment_size_order]);
> -	}
> -	grp->bb_avg_fragment_size_order = new_order;
> -	write_lock(&sbi->s_mb_avg_fragment_size_locks[
> -					grp->bb_avg_fragment_size_order]);
> -	list_add_tail(&grp->bb_avg_fragment_size_node,
> -		&sbi->s_mb_avg_fragment_size[grp->bb_avg_fragment_size_order]);
> -	write_unlock(&sbi->s_mb_avg_fragment_size_locks[
> -					grp->bb_avg_fragment_size_order]);
> +		write_unlock(&sbi->s_mb_avg_fragment_size_locks[old]);
> +	}
> +
> +	grp->bb_avg_fragment_size_order = new;
> +	if (new >= 0) {
> +		write_lock(&sbi->s_mb_avg_fragment_size_locks[new]);
> +		list_add_tail(&grp->bb_avg_fragment_size_node,
> +				&sbi->s_mb_avg_fragment_size[new]);
> +		write_unlock(&sbi->s_mb_avg_fragment_size_locks[new]);
> +	}
>  }
>  
>  /*
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR