Re: [PATCH v2 4/8] ext4: avoid bb_free and bb_fragments inconsistency in mb_free_blocks()

[Baokun Li <libaokun1@huawei.com>]

On 2024/1/4 18:42, Jan Kara wrote:
> 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
Yes, it looks much clearer that way!
I will switch to it in the next version.

Thanks a lot!
-- 
With Best Regards,
Baokun Li
.