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Re: synchronization of XFS

To: Steve Lord <lord@xxxxxxx>
Subject: Re: synchronization of XFS
From: Stefan Smietanowski <stesmi@xxxxxxxxxx>
Date: Thu, 25 Mar 2004 23:49:22 +0100
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Chris Wedgwood <cw@xxxxxxxx>, "IKARASHI, Seiichi" <ikarashi@xxxxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
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Hi Steve.

>>>>>> Now if grub is opening the block device and reading out of that, it
>>>>>> is looking at the same pages for metadata that xfs is looking at in
>>>>>> memory. There is a bug where you can get corruption if you access
>>>>>> the block device in parallel with the filesystem. Possibly this is
>>>>>> behind the problem.
>>>>> This will cause an oops on 2.6.x won't it --- so I suspect if this is
>>>>> behind the problem the report will be have been different.
>>>> I don't think they're hitting the problem, the symptoms look very 
>>>> different.
>>> And thinking about it some more, having grub make the filesystem 
>>> remount readonly would force everything down to disk unlike just 
>>> doing a sync
>>> call.
>> Tried and failed :(
>> Tried that before but it didn't help unfortunately.
> So what exactly is the sequence of events here, some files are created
> in the boot directory via the kernel, then grub wants to look at them
> via the block device api and its emulation of the filesystem? If we
> can nail this down, then maybe we can really work out what is going
> on here.
> Steve

Yup. That's what's happening. It first does one run with --just-copy
where it writes the files using the filesystem then reads the same
files using the blockdevice and it's own filesystem code basically.

// Stefan

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