linux-ext4 - Re: [PATCH v2 3/8] ext4: regenerate buddy after block freeing failed if under fc replay

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Message-ID: <20240104103336.fjwhqiv2maezquef@quack3>
Date: Thu, 4 Jan 2024 11:33:36 +0100
From: Jan Kara <jack@...e.cz>
To: Baokun Li <libaokun1@...wei.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
	jack@...e.cz, ritesh.list@...il.com, linux-kernel@...r.kernel.org,
	yi.zhang@...wei.com, yangerkun@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 3/8] ext4: regenerate buddy after block freeing failed
 if under fc replay

On Thu 21-12-23 23:05:53, Baokun Li wrote:
> This reverts [Fixes] under fast commit replay. When we are freeing blocks
> that have already been freed, the buddy may be corrupted, and we need to
> regenerate the buddy when the fast commit is being replayed in order to
> avoid using an corrupted buddy, since it will not mark the group block
> bitmap as corrupted at that point.

I'd rephrase the changelog as:

This mostly reverts commit 6bd97bf273bd ("ext4: remove redundant
mb_regenerate_buddy()") and reintroduces mb_regenerate_buddy(). Based on
code in mb_free_blocks(), fast commit replay can end up marking as free
blocks that are already marked as such. This causes corruption of the
buddy bitmap so we need to regenerate it in that case.

Otherwise the patch looks good to me so feel free to add:

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

								Honza
> 
> Reported-by: Jan Kara <jack@...e.cz>
> Fixes: 6bd97bf273bd ("ext4: remove redundant mb_regenerate_buddy()")
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ---
>  fs/ext4/mballoc.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index a95fa6e2b0f9..f6131ba514c8 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -1233,6 +1233,24 @@ void ext4_mb_generate_buddy(struct super_block *sb,
>  	atomic64_add(period, &sbi->s_mb_generation_time);
>  }
>  
> +static void mb_regenerate_buddy(struct ext4_buddy *e4b)
> +{
> +	int count;
> +	int order = 1;
> +	void *buddy;
> +
> +	while ((buddy = mb_find_buddy(e4b, order++, &count)))
> +		mb_set_bits(buddy, 0, count);
> +
> +	e4b->bd_info->bb_fragments = 0;
> +	memset(e4b->bd_info->bb_counters, 0,
> +		sizeof(*e4b->bd_info->bb_counters) *
> +		(e4b->bd_sb->s_blocksize_bits + 2));
> +
> +	ext4_mb_generate_buddy(e4b->bd_sb, e4b->bd_buddy,
> +		e4b->bd_bitmap, e4b->bd_group, e4b->bd_info);
> +}
> +
>  /* The buddy information is attached the buddy cache inode
>   * for convenience. The information regarding each group
>   * is loaded via ext4_mb_load_buddy. The information involve
> @@ -1921,6 +1939,8 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
>  			ext4_mark_group_bitmap_corrupted(
>  				sb, e4b->bd_group,
>  				EXT4_GROUP_INFO_BBITMAP_CORRUPT);
> +		} else {
> +			mb_regenerate_buddy(e4b);
>  		}
>  		goto done;
>  	}
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR