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Subject: Re: 2.6.19 file content corruption on ext3
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andrew Morton <akpm@osdl.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, Linus Torvalds <torvalds@osdl.org>,
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Date: Tue, 19 Dec 2006 11:52:15 +0100
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On Tue, 2006-12-19 at 02:32 -0800, Andrew Morton wrote:
> On Tue, 19 Dec 2006 20:56:50 +1100
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
> > Linus Torvalds wrote:
> > 
> > > NOTICE? First you make a BIG DEAL about how dirty bits should never get 
> > > lost, but THE VERY SAME FUNCTION actually very much on purpose DOES drop 
> > > the dirty bit for when it's not in the page tables.
> > 
> > try_to_free_buffers is quite a special case, where we're transferring
> > the page dirty metadata from the buffers to the page. I think Andrew
> > would have a better grasp of it so he could correct me, but what it
> > does is legitimate.
> 
> Well it used to be.  After 2.6.19 it can do the wrong thing for mapped
> pages.  But it turns out that we don't feed it mapped pages, apart from
> pagevec_strip() and possibly races against pagefaults.

So how about this:

Index: linux-2.6-git/mm/page-writeback.c
===================================================================
--- linux-2.6-git.orig/mm/page-writeback.c	2006-12-19 08:24:48.000000000 +0100
+++ linux-2.6-git/mm/page-writeback.c	2006-12-19 11:43:31.000000000 +0100
@@ -859,6 +859,9 @@ int test_clear_page_dirty(struct page *p
 	struct address_space *mapping = page_mapping(page);
 	unsigned long flags;
 
+	if (page_mapped(page))
+		return 0;
+
 	if (!mapping)
 		return TestClearPageDirty(page);