linux-kernel - Re: [Ocfs2-devel] [PATCH v2 4/4] ocfs2: check/fix inode block for online file check

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Date:	Tue, 24 Nov 2015 22:04:00 -0700
From:	"Gang He" <ghe@...e.com>
To:	"Junxiao Bi" <junxiao.bi@...cle.com>,
	"Mark Fasheh" <mfasheh@...e.de>
Cc:	<ocfs2-devel@....oracle.com>, <rgoldwyn@...e.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Ocfs2-devel] [PATCH v2 4/4] ocfs2: check/fix inode block
 for online file check

Hi Mark and Junxiao,


>>> 
> Hi Mark,
> 
> On 11/25/2015 06:16 AM, Mark Fasheh wrote:
>> Hi Junxiao,
>> 
>> On Tue, Nov 03, 2015 at 03:12:35PM +0800, Junxiao Bi wrote:
>>> Hi Gang,
>>>
>>> This is not like a right patch.
>>> First, online file check only checks inode's block number, valid flag,
>>> fs generation value, and meta ecc. I never see a real corruption
>>> happened only on this field, if these fields are corrupted, that means
>>> something bad may happen on other place. So fix this field may not help
>>> and even cause corruption more hard.
>> 
>> I agree that these are rather uncommon, we might even consider removing the
>> VALID_FL fixup. I definitely don't think we're ready for anything more
>> complicated than this though either. We kind of have to start somewhere too.
>> 
> Yes, the fix is too simple, and just a start, I think we'd better wait
> more useful parts done before merging it.
I agree, just remark VALID_FL flag to fix this field is too simple, we should delay this field fix before 
I have a flawless solution, I will remove these lines code in the first version patches. In the future submits,
I also hope your guys to help review the code carefully, shout out your comments when you doubt somewhere.



>> 
>>> Second, the repair way is wrong. In
>>> ocfs2_filecheck_repair_inode_block(), if these fields in disk don't
>>> match the ones in memory, the ones in memory are used to update the disk
>>> fields. The question is how do you know these field in memory are
>>> right(they may be the real corrupted ones)?
>> 
>> Your second point (and the last part of your 1st point) makes a good
>> argument for why this shouldn't happen automatically. Some of these
>> corruptions might require a human to look at the log and decide what to do.
>> Especially as you point out, where we might not know where the source of the
>> corruption is. And if the human can't figure it out, then it's probably time
>> to unmount and fsck.
> The point is that the fix way is wrong, just flush memory info to disk
> is not right. I agree online fsck is good feature, but need carefully
> design, it should not involve more corruptions. A rough idea from mine
> is that maybe we need some "frezee" mechanism in fs, which can hung all
> fs op and let fs stop at a safe area. After freeze fs, we can do some
> fsck work on it and these works should not cost lots time. What's your idea?
If we need to touch some global data structures, freezing fs can be considered when we can't
get any way in case using the locks.
If we only handle some independent problem, we just need to lock the related data structures. 

> 
> Thanks,
> Junxiao.
> 
>> 
>> Thanks,
>> 	--Mark
>> 
>> --
>> Mark Fasheh
>> 

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