linux-ext4 - Re: [PATCH v2] ext4: increase i_disksize to offset + len in ext4_update_disksize_before

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Message-ID: <a52708a8-cb3f-41bb-b73c-7d19f4830709@huawei.com>
Date: Tue, 9 Sep 2025 19:30:43 +0800
From: Sun Yongjian <sunyongjian1@...wei.com>
To: Zhang Yi <yi.zhang@...weicloud.com>, <linux-ext4@...r.kernel.org>
CC: <linux-fsdevel@...r.kernel.org>, <tytso@....edu>, <jack@...e.cz>,
	<yangerkun@...wei.com>, <libaokun1@...wei.com>, <chengzhihao1@...wei.com>
Subject: Re: [PATCH v2] ext4: increase i_disksize to offset + len in
 ext4_update_disksize_before_punch()



在 2025/9/8 15:58, Zhang Yi 写道:
> On 9/8/2025 2:33 PM, Yongjian Sun wrote:
>> From: Yongjian Sun <sunyongjian1@...wei.com>
>>
>> After running a stress test combined with fault injection,
>> we performed fsck -a followed by fsck -fn on the filesystem
>> image. During the second pass, fsck -fn reported:
>>
>> Inode 131512, end of extent exceeds allowed value
>> 	(logical block 405, physical block 1180540, len 2)
>>
>> This inode was not in the orphan list. Analysis revealed the
>> following call chain that leads to the inconsistency:
>>
>>                               ext4_da_write_end()
>>                                //does not update i_disksize
>>                               ext4_punch_hole()
>>                                //truncate folio, keep size
>> ext4_page_mkwrite()
>>   ext4_block_page_mkwrite()
>>    ext4_block_write_begin()
>>      ext4_get_block()
>>       //insert written extent without update i_disksize
>> journal commit
>> echo 1 > /sys/block/xxx/device/delete
>>
>> da-write path updates i_size but does not update i_disksize. Then
>> ext4_punch_hole truncates the da-folio yet still leaves i_disksize
>> unchanged(in the ext4_update_disksize_before_punch function, the
>> condition offset + len < size is met). Then ext4_page_mkwrite sees
>> ext4_nonda_switch return 1 and takes the nodioread_nolock path, the
>> folio about to be written has just been punched out, and it’s offset
>> sits beyond the current i_disksize. This may result in a written
>> extent being inserted, but again does not update i_disksize. If the
>> journal gets committed and then the block device is yanked, we might
>> run into this. It should be noted that replacing ext4_punch_hole with
>> ext4_zero_range in the call sequence may also trigger this issue, as
>> neither will update i_disksize under these circumstances.
>>
>> To fix this, we can modify ext4_update_disksize_before_punch to always
>> increase i_disksize to offset + len.
>>
>> Signed-off-by: Yongjian Sun <sunyongjian1@...wei.com>
>> ---
>> Changes in v2:
>> - The modification of i_disksize should be moved into ext4_update_disksize_before_punch,
>>    rather than being done in ext4_page_mkwrite.
>> - Link to v1: https://lore.kernel.org/all/20250731140528.1554917-1-sunyongjian@huaweicloud.com/
>> ---
>>   fs/ext4/inode.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index 5b7a15db4953..2b1ed729a0f0 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -4298,7 +4298,7 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
>>   	loff_t size = i_size_read(inode);
>>   
>>   	WARN_ON(!inode_is_locked(inode));
>> -	if (offset > size || offset + len < size)
>> +	if (offset > size)
>>   		return 0;
>>   
>>   	if (EXT4_I(inode)->i_disksize >= size)
> 
> Hi, Yongjian!
> 
> I think this check also needs to be updated; otherwise, the limitation
> will be too lenient. If the end position of the punch hole
> is <= i_disksize, we should also avoid updating the i_disksize (this is
> a more general use case). Besides, I'd suggested updating the comment
> of ext4_update_disksize_before_punch() together.
> 
> Regards,
> Yi.
> 

Hi!

Thanks for the review! I agree with that and will send out the v3 ASAP ^_^

Cheers!

>> @@ -4307,7 +4307,7 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
>>   	handle = ext4_journal_start(inode, EXT4_HT_MISC, 1);
>>   	if (IS_ERR(handle))
>>   		return PTR_ERR(handle);
>> -	ext4_update_i_disksize(inode, size);
>> +	ext4_update_i_disksize(inode, min_t(loff_t, size, offset + len));
>>   	ret = ext4_mark_inode_dirty(handle, inode);
>>   	ext4_journal_stop(handle);
>>   
>