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

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Date:	Wed, 25 Nov 2015 12:11:01 +0800
From:	Junxiao Bi <junxiao.bi@...cle.com>
To:	Mark Fasheh <mfasheh@...e.de>
Cc:	Gang He <ghe@...e.com>, rgoldwyn@...e.de,
	linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v2 4/4] ocfs2: check/fix inode block for
 online file check

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.
> 
>> 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?

Thanks,
Junxiao.

> 
> Thanks,
> 	--Mark
> 
> --
> Mark Fasheh
> 

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