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Date:	Mon, 18 Jan 2010 14:51:46 +1100
From:	Nick Piggin <npiggin@...e.de>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	stable@...nel.org
Subject: Re: [PATCH] vfs: Fix vmtruncate() regression

On Fri, Jan 15, 2010 at 09:26:02AM +0900, OGAWA Hirofumi wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
> 
> > On Wed, 13 Jan 2010 21:14:09 +0900
> > OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> wrote:
> >
> >> 
> >> If __block_prepare_write() was failed in block_write_begin(), the
> >> allocated blocks can be outside of ->i_size.
> >> 
> >> But new truncate_pagecache() in vmtuncate() does nothing if new < old.
> >> It means the above usage is not working anymore.
> >> 
> >> So, this patch fixes it by removing "new < old" check. It would need
> >> more cleanup/change. But, now -rc and truncate working is in progress,
> >> so, this tried to fix it minimum change.
> >> 
> >> Acked-by: Nick Piggin <npiggin@...e.de>
> >> Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> >> ---
> >> 
> >>  mm/truncate.c |   28 +++++++++++++---------------
> >>  1 file changed, 13 insertions(+), 15 deletions(-)
> >> 
> >> diff -puN mm/truncate.c~truncate_pagecache-fix mm/truncate.c
> >> --- linux-2.6/mm/truncate.c~truncate_pagecache-fix	2010-01-12 05:43:06.000000000 +0900
> >> +++ linux-2.6-hirofumi/mm/truncate.c	2010-01-12 05:43:06.000000000 +0900
> >> @@ -522,22 +522,20 @@ EXPORT_SYMBOL_GPL(invalidate_inode_pages
> >>   */
> >>  void truncate_pagecache(struct inode *inode, loff_t old, loff_t new)
> >>  {
> >> -	if (new < old) {
> >> -		struct address_space *mapping = inode->i_mapping;
> >> +	struct address_space *mapping = inode->i_mapping;
> >>  
> >> -		/*
> >> -		 * unmap_mapping_range is called twice, first simply for
> >> -		 * efficiency so that truncate_inode_pages does fewer
> >> -		 * single-page unmaps.  However after this first call, and
> >> -		 * before truncate_inode_pages finishes, it is possible for
> >> -		 * private pages to be COWed, which remain after
> >> -		 * truncate_inode_pages finishes, hence the second
> >> -		 * unmap_mapping_range call must be made for correctness.
> >> -		 */
> >> -		unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
> >> -		truncate_inode_pages(mapping, new);
> >> -		unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
> >> -	}
> >> +	/*
> >> +	 * unmap_mapping_range is called twice, first simply for
> >> +	 * efficiency so that truncate_inode_pages does fewer
> >> +	 * single-page unmaps.  However after this first call, and
> >> +	 * before truncate_inode_pages finishes, it is possible for
> >> +	 * private pages to be COWed, which remain after
> >> +	 * truncate_inode_pages finishes, hence the second
> >> +	 * unmap_mapping_range call must be made for correctness.
> >> +	 */
> >> +	unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
> >> +	truncate_inode_pages(mapping, new);
> >> +	unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
> >>  }
> >>  EXPORT_SYMBOL(truncate_pagecache);
> >
> > The fix was applied to 2.6.33-rcX
> > (cedabed49b39b4319bccc059a63344b6232b619c), appears to be needed in
> > 2.6.32.x but no cc:stable's are present?
> 
> Ah, yes. I forgot to add "Cc: stable". Please apply this to 2.6.32.x.

Thanks guys, it's quite important so please apply to stable 2.6.32 and
consider it as a high priority to release.

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