linux-kernel - Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk

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Date:	Thu, 14 Jun 2007 15:01:19 -0400
From:	Phillip Susi <psusi@....rr.com>
To:	Pavel Machek <pavel@....cz>
CC:	Mark Lord <lkml@....ca>, Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Tweedie <sct@...hat.com>,
	Theodore Ts'o <tytso@....edu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk

Pavel Machek wrote:
> Hi!
> 
>>> Did this succeed?  If the application is still 
>>> truncating that file, the
>>> umount should have failed.
>> Actually, what I expect to happen is for the remount,ro
>> to block  until the file deletion completes.  But it 
>> doesn't.
>>
>> Once a f/s is read-only, there should be NO writing to 
>> it.  Right?
> 
> Linux happily writes to filesystems mounted read-only. It will replay
> journal on them.

That's a bug and needs fixed.  Read only means read _only_.

And the question still remains; why is sync() not blocking until the 
file has been completely unlinked and the disk is consistent?
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