Re: [RFC][PATCH] HWPOISON: remove the unsafe __set_page_locked()

[Andi Kleen <andi@firstfloor.org>]

On Mon, Sep 28, 2009 at 04:57:41AM +0200, Nick Piggin wrote:
> 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.

Yes, currently the page lock comes first. The only exception 
is for page count == 0 pages. I suppose we could move the slab check
up, but then it only helps when slab is set.

So if you make slab use refcount == 0 pages that would help.

> Well it's fundamentally badly buggy, rare or not. We could avoid

Let's put it like this -- any access to the poisoned cache lines
in that page will trigger a panic anyways.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.