linux-kernel - Re: [RFC][PATCH] HWPOISON: remove the unsafe __set_page

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Date:	Mon, 28 Sep 2009 04:57:41 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] HWPOISON: remove the unsafe __set_page_locked()

On Mon, Sep 28, 2009 at 03:19:43AM +0200, Andi Kleen wrote:
> > There is no real rush AFAIKS to fix this one single pagecache site
> > while we have problems with slab allocators and all other unaudited
> > places that nonatomically modify page flags with an elevated
> 
> hwpoison ignores slab pages.

"ignores" them *after* it has already written to page flags?
By that time it's too late.

 
> > page reference ... just mark HWPOISON as broken for the moment, or
> > cut it down to do something much simpler I guess?
> 
> Erm no. These cases are *EXTREMLY* unlikely to hit.

Well it's fundamentally badly buggy, rare or not. We could avoid
lots of nasty atomic operations if we just care that it works
most of the time. I guess it's a matter of perspective but I
won't push for one thing or the other in hwpoison code so long
as it stays out of core code for the most part.

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