linux-kernel - Re: [stable] [patch 07/19] invalidate_complete

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Date:	Tue, 10 Oct 2006 12:30:27 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Greg KH <greg@...ah.com>
Cc:	Hugh Dickins <hugh@...itas.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	"Theodore Ts'o" <tytso@....edu>,
	Zwane Mwaikambo <zwane@....linux.org.uk>, torvalds@...l.org,
	Greg KH <gregkh@...e.de>, Justin Forbes <jmforbes@...uxtx.org>,
	linux-kernel@...r.kernel.org,
	Chris Wedgwood <reviews@...cw.f00f.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Michael Krufky <mkrufky@...uxtv.org>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>, stable@...nel.org,
	alan@...rguk.ukuu.org.uk
Subject: Re: [stable] [patch 07/19] invalidate_complete_page() race fix

On Tue, 10 Oct 2006 12:14:18 -0700
Greg KH <greg@...ah.com> wrote:

> On Tue, Oct 10, 2006 at 07:12:54PM +0100, Hugh Dickins wrote:
> > On Tue, 10 Oct 2006, Greg KH wrote:
> > 
> > > -stable review patch.  If anyone has any objections, please let us know.
> > > 
> > > ------------------
> > > From: Andrew Morton <akpm@...l.org>
> > > 
> > > If a CPU faults this page into pagetables after invalidate_mapping_pages()
> > > checked page_mapped(), invalidate_complete_page() will still proceed to remove
> > > the page from pagecache.  This leaves the page-faulting process with a
> > > detached page.  If it was MAP_SHARED then file data loss will ensue.
> > > 
> > > Fix that up by checking the page's refcount after taking tree_lock.
> > 
> > I may have lost the plot, but I think this patch has already proved
> > to cause problems for NFS in 2.6.18: not good to put it into 2.6.17
> > stable while it's awaiting refinement for 2.6.18 stable.
> 
> Ok, I've dropped it now.
> 

It needs invalidate_inode_pages2-ignore-page-refcounts.patch as well.

This patch (invalidate_complete_page() race fix) fixes a cramfs unmount
race and, iirc, a pagefault-vs-invalidate race which Nick was seeing.
So applying both patches would make 2.6.17 a better place, but we could live
without them.
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