linux-kernel - Re: [PATCH v2 1/3] ext4: fix incorrect calculate 'reserved' in '__es_remove

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Date:   Fri, 2 Dec 2022 14:00:02 +0800
From:   "yebin (H)" <yebin10@...wei.com>
To:     Eric Whitney <enwlinux@...il.com>, Ye Bin <yebin@...weicloud.com>
CC:     <tytso@....edu>, <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <jack@...e.cz>,
        <syzbot+05a0f0ccab4a25626e38@...kaller.appspotmail.com>
Subject: Re: [PATCH v2 1/3] ext4: fix incorrect calculate 'reserved' in
 '__es_remove_extent' when enable bigalloc feature



On 2022/12/2 6:21, Eric Whitney wrote:
> * Ye Bin <yebin@...weicloud.com>:
>> From: Ye Bin <yebin10@...wei.com>
>>
>> Syzbot report issue as follows:
>> EXT4-fs error (device loop0): ext4_validate_block_bitmap:398: comm rep: bg 0: block 5: invalid block bitmap
>> EXT4-fs (loop0): Delayed block allocation failed for inode 18 at logical offset 0 with max blocks 32 with error 28
>> EXT4-fs (loop0): This should not happen!! Data will be lost
>>
>> EXT4-fs (loop0): Total free blocks count 0
>> EXT4-fs (loop0): Free/Dirty block details
>> EXT4-fs (loop0): free_blocks=0
>> EXT4-fs (loop0): dirty_blocks=32
>> EXT4-fs (loop0): Block reservation details
>> EXT4-fs (loop0): i_reserved_data_blocks=2
>> EXT4-fs (loop0): Inode 18 (00000000845cd634): i_reserved_data_blocks (1) not cleared!
>>
>> Above issue happens as follows:
>> Assume:
>> sbi->s_cluster_ratio = 16
>> Step1: Insert delay block [0, 31] -> ei->i_reserved_data_blocks=2
>> Step2:
>> ext4_writepages
>>    mpage_map_and_submit_extent -> return failed
>>    mpage_release_unused_pages -> to release [0, 30]
>>      ext4_es_remove_extent -> remove lblk=0 end=30
>>        __es_remove_extent -> len1=0 len2=31-30=1
>>   __es_remove_extent:
>>   ...
>>   if (len2 > 0) {
>>    ...
>> 	  if (len1 > 0) {
>> 		  ...
>> 	  } else {
>> 		es->es_lblk = end + 1;
>> 		es->es_len = len2;
>> 		...
>> 	  }
>>    	if (count_reserved)
>> 		count_rsvd(inode, lblk, orig_es.es_len - len1 - len2, &orig_es, &rc);
>> 	goto out; -> will return but didn't calculate 'reserved'
>>   ...
>> Step3: ext4_destroy_inode -> trigger "i_reserved_data_blocks (1) not cleared!"
>>
>> To solve above issue if 'len2>0' call 'get_rsvd()' before goto out.
>>
>> Reported-by: syzbot+05a0f0ccab4a25626e38@...kaller.appspotmail.com
>> Signed-off-by: Ye Bin <yebin10@...wei.com>
>> ---
>>   fs/ext4/extents_status.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
>> index cd0a861853e3..4684eaea9471 100644
>> --- a/fs/ext4/extents_status.c
>> +++ b/fs/ext4/extents_status.c
>> @@ -1371,7 +1371,7 @@ static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>>   		if (count_reserved)
>>   			count_rsvd(inode, lblk, orig_es.es_len - len1 - len2,
>>   				   &orig_es, &rc);
>> -		goto out;
>> +		goto count;
>>   	}
>>   
>>   	if (len1 > 0) {
>> @@ -1413,6 +1413,7 @@ static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>>   		}
>>   	}
>>   
>> +count:
>>   	if (count_reserved)
>>   		*reserved = get_rsvd(inode, end, es, &rc);
>>   out:
>> -- 
>> 2.31.1
>>
> I'm unable to find the sysbot report for this patch, so I can't verify that
> this fix works.  The more serious problem would be whatever is causing
> the invalid block bitmap and delayed allocation failure messages before the
> i_reserved_data_blocks message.  Perhaps that's simply what syzkaller set
> up, but it's not clear from this posting.  Have you looked for the cause
> of those first two messages?
>
> However, by inspection this patch should fix an obvious bug causing that last
> message, introduced by 8fcc3a580651 ("ext4: rework reserved cluster accounting
> when invalidating pages").  A Fixes tag should be added to the patch.  Also,
> the readability of the code should be improved by changing the label "count" to
> the more descriptive "out_get_reserved".
>
> With those two changes, feel free to add:
>
> Reviewed-by: Eric Whitney <enwlinux@...il.com>
>
> Eric
> .

Thanks for your suggestion. I will send another version.