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Date: Thu, 4 Jan 2024 11:42:55 +0100
From: Jan Kara <jack@suse.cz>
To: Baokun Li <libaokun1@huawei.com>
Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca,
	jack@suse.cz, ritesh.list@gmail.com, linux-kernel@vger.kernel.org,
	yi.zhang@huawei.com, yangerkun@huawei.com, yukuai3@huawei.com,
	stable@vger.kernel.org
Subject: Re: [PATCH v2 4/8] ext4: avoid bb_free and bb_fragments
 inconsistency in mb_free_blocks()
Message-ID: <20240104104255.eewvmywxyqtfwzug@quack3>
References: <20231221150558.2740823-1-libaokun1@huawei.com>
 <20231221150558.2740823-5-libaokun1@huawei.com>
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In-Reply-To: <20231221150558.2740823-5-libaokun1@huawei.com>

On Thu 21-12-23 23:05:54, Baokun Li wrote:
> 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
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Just one nit below but regardless of that feel free to add:

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

> @@ -1941,10 +1936,16 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
>  				EXT4_GROUP_INFO_BBITMAP_CORRUPT);
>  		} else {
>  			mb_regenerate_buddy(e4b);
> +			goto check;
>  		}
> -		goto done;
> +		return;
>  	}

I think this might be more readable when we revert the condition like:

		/*
		 * 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;
		}
                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);
		return;
	}

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR