Re: [PATCH v3 1/2] ext4: commit super block if fs record error when journal record without error

["yebin (H)" <yebin10@huawei.com>]

On 2023/2/27 19:20, Jan Kara wrote:
> On Sat 18-02-23 10:18:42, yebin (H) wrote:
>> On 2023/2/17 18:56, Jan Kara wrote:
>>> On Fri 17-02-23 09:44:57, yebin (H) wrote:
>>>> On 2023/2/17 1:31, Jan Kara wrote:
>>>>> On Tue 14-02-23 10:29:04, Ye Bin wrote:
>>>>>> From: Ye Bin <yebin10@huawei.com>
>>>>>>
>>>>>> Now, 'es->s_state' maybe covered by recover journal. And journal errno
>>>>>> maybe not recorded in journal sb as IO error. ext4_update_super() only
>>>>>> update error information when 'sbi->s_add_error_count' large than zero.
>>>>>> Then 'EXT4_ERROR_FS' flag maybe lost.
>>>>>> To solve above issue commit error information after recover journal.
>>>>>>
>>>>>> Signed-off-by: Ye Bin <yebin10@huawei.com>
>>>>>> ---
>>>>>>     fs/ext4/super.c | 12 ++++++++++++
>>>>>>     1 file changed, 12 insertions(+)
>>>>>>
>>>>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>>>>> index dc3907dff13a..b94754ba8556 100644
>>>>>> --- a/fs/ext4/super.c
>>>>>> +++ b/fs/ext4/super.c
>>>>>> @@ -5932,6 +5932,18 @@ static int ext4_load_journal(struct super_block *sb,
>>>>>>     		goto err_out;
>>>>>>     	}
>>>>>> +	if (unlikely(es->s_error_count && !jbd2_journal_errno(journal) &&
>>>>>> +		     !(le16_to_cpu(es->s_state) & EXT4_ERROR_FS))) {
>>>>>> +		EXT4_SB(sb)->s_mount_state |= EXT4_ERROR_FS;
>>>>>> +		es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
>>>>>> +		err = ext4_commit_super(sb);
>>>>>> +		if (err) {
>>>>>> +			ext4_msg(sb, KERN_ERR,
>>>>>> +				 "Failed to commit error information, please repair fs force!");
>>>>>> +			goto err_out;
>>>>>> +		}
>>>>>> +	}
>>>>>> +
>>>>> Hum, I'm not sure I follow here. If journal replay has overwritten the
>>>>> superblock (and thus the stored error info), then I'd expect
>>>>> es->s_error_count got overwritten (possibly to 0) as well. And this is
>>>>> actually relatively realistic scenario with errors=remount-ro behavior when
>>>>> the first fs error happens.
>>>>>
>>>>> What I intended in my original suggestion was to save es->s_error_count,
>>>>> es->s_state & EXT4_ERROR_FS, es->s_first_error_*, es->s_last_error_* before
>>>>> doing journal replay in ext4_load_journal() and then after journal replay
>>>>> merge this info back to the superblock
>>>> Actually，commit 1c13d5c08728 ("ext4: Save error information to the
>>>> superblock for analysis")
>>>> already merged error info back to the superblock after journal replay except
>>>> 'es->s_state'.
>>>> The problem I have now is that the error flag in the journal superblock was
>>>> not recorded,
>>>> but the error message was recorded in the superblock. So it leads to
>>>> ext4_clear_journal_err()
>>>> does not detect errors and marks the file system as an error. Because
>>>> ext4_update_super() is
>>>> only set error flag  when 'sbi->s_add_error_count  > 0'. Although
>>>> 'sbi->s_mount_state' is
>>>> written to the super block when umount, but it is also conditional.
>>>> So I handle the scenario "es->s_error_count && !jbd2_journal_errno(journal)
>>>> &&
>>>> !(le16_to_cpu(es->s_state) & EXT4_ERROR_FS)". Maybe we can just store
>>>> 'EXT4_SB(sb)->s_mount_state & EXT4_ERROR_FS' back to the superblock. But i
>>>> prefer to mark fs as error if it contain detail error info without
>>>> EXT4_ERROR_FS.
>>> Aha, thanks for explanation! So now I finally understand what the problem
>>> exactly is. I'm not sure relying on es->s_error_count is too good. Probably
>>> it works but I'd be calmer if when saving error info we also did:
>>>
>>> 	bool error_fs = es->s_state & cpu_to_le16(EXT4_ERROR_FS);
>>>
>>> 	copy other info
>>> 	err = jbd2_journal_load(journal);
>>> 	restore other info
>>> 	if (error_fs)
>>> 		es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
>>> 	/* Write out restored error information to the superblock */
>>> 	err2 = ext4_commit_super(sb);
>>>
>>> and be done with this. I don't think trying to optimize away the committing
>>> of the superblock when we had to replay the journal is really worth it.
>>>
>>> Does this solve your concerns?
>> Thanks for your suggestion.
>>
>> I think if journal super block has 'j_errno' ext4_clear_journal_err()
>> will commit error info.  The scenario we need to deal with is:(1) journal
>> super block has no 'j_errno'; (2) super block has detail error info, but
>> 'es->s_state' has no 'EXT4_ERROR_FS', It means super block in journal has
>> no error flag and the newest super block has error flag.
> But my code above should be handling this situation you describe - the
> check:
>
> error_fs = es->s_state & cpu_to_le16(EXT4_ERROR_FS);
Here, we do not need to backup 'error_fs', as 
'EXT4_SB(sb)->s_mount_state' already
record this flag when fs has error flag before do journal replay.
> will check the newest state in the superblock before journal replay. Then
> we replay the journal - es->s_state may loose the EXT4_ERROR_FS flag if the
> superblock version in the journal didn't have it. So we do:
>
> if (error_fs)
> 	es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
>
> which makes sure EXT4_ERROR_FS is set either if it was set in the journal
> or in the newest superblock version before journal replay.
My modification is to deal with the situation we missed, and I don't 
want to introduce
an invalid super block submission.
If you think my judgment is too obscure, I can send another version 
according to your
suggestion.
>> so we need to
>> store error flag to 'es->s_state', and commit it to disk.If 'es->s_state'
>> has 'EXT4_ERROR_FS', it means super block in journal has error flag, so
>> we do not need to store error flag in super block.
> Why do you think that if es->s_state has EXT4_ERROR_FS, the super block in
> the journal has that flag? During mount, we load the superblock directly
> from the first block in the filesystem and until we call
> jbd2_journal_load(), es->s_state contains this newest value of the
> superblock state. What am I missing?
After jbd2_journal_load() 'es->s_state' is already covered by the super 
block in journal.
If there is super block in journal and 'es->s_state' has error flag this 
means super block
in journal has error flag. If there is no super block in journal and  
'es->s_state' has error
flag, this means super block already has error flag.In both cases we can 
do nothing.
>
> 								Honza