linux-kernel - Re: 2.6.19 file content corruption on ext3

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Message-ID: <Pine.LNX.4.64.0612182230301.3479@woody.osdl.org>
Date:	Mon, 18 Dec 2006 22:34:14 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...l.org>, andrei.popa@...eo.ro,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Martin Michlmayr <tbm@...ius.com>
Subject: Re: 2.6.19 file content corruption on ext3



On Tue, 19 Dec 2006, Nick Piggin wrote:
> 
> We never want to drop dirty data! (ignoring the truncate case, which is
> handled privately by truncate anyway)

Bzzt.

SURE we do.

We absolutely do want to drop dirty data in the writeout path.

How do you think dirty data ever _becomes_ clean data?

In other words, yes, we _do_ want to test-and-clear all the pgtable bits 
_and_ the PG_dirty bit. We want to do it for:
 - writeout
 - truncate
 - possibly a "drop" event (which could be a case for a journal entry that 
   becomes stale due to being replaced or something - kind of "truncate" 
   on metadata)

because both of those events _literally_ turn dirty state into clean 
state.

In no other circumstance do we ever want to clear a dirty bit, as far as I 
can tell. 

			Linus
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