linux-kernel - Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again

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Date:	Mon, 1 Jan 2007 16:21:42 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	James Bottomley <James.Bottomley@...elEye.com>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...l.org>
Subject: Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again

On Mon, Jan 01, 2007 at 09:35:17AM -0500, James Bottomley wrote:
> On Sat, 2006-12-30 at 10:26 -0800, Linus Torvalds wrote:
> > 
> > On Sat, 30 Dec 2006, Russell King wrote:
> > > 
> > > And here's the flush_anon_page() part.
> 
> This looks fine to me (if you need my ack).
> 
> > > Add flush_anon_page() for ARM, to avoid data corruption issues when using
> > > fuse or other subsystems using get_user_pages().
> > 
> > Btw, since this doesn't actually change any code for anybody but ARM, just 
> > adds a parameter that is obviously unused by everybody else, and if it 
> > actually fixes a real bug for ARM, I'll obviously happily take it even 
> > before 2.6.20. So go ahead put it in your ARM tree, and we'll get some 
> > testing through that. And just ask me to pull at some point.
> > 
> > I wonder why nobody else seems to have a "flush_anon_page()"? This would 
> > seem to be a potential issue for architectures like sparc too.. Although 
> > maybe sparc can do a flush by physical index with "flush_dcache_page()".
> 
> The sparc handling of anonymous pages is different ... they accitentally
> sweep them up in flush_dcache_page().  When I audited the architectures
> to try to make fuse work on parisc, parisc and arm were the only ones
> that actually needed flush_anon_page().

However, as David has said, anonymous pages _are_ supposed to be handled
by flush_dcache_page(), so I now have an (untested) implementation for
ARM which does this.  Therefore, I'm revoking the previous two patches.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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