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SubjectRe: [PATCH 10/22] HWPOISON: check and isolate corrupted free pages v2
On Tue, Jun 16, 2009 at 07:29:45PM +0800, Hugh Dickins wrote:
> On Tue, 16 Jun 2009, Wu Fengguang wrote:
> >
> > Right. Then the original __ClearPageBuddy() call in bad_page() is
> > questionable, I guess this line was there just for the sake of safety
> > (ie. the buddy allocator itself goes wrong):
> >
> > sound-2.6/mm/page_alloc.c
> >
> > @@ -269,7 +269,6 @@ static void bad_page(struct page *page)
> > dump_stack();
> > out:
> > /* Leave bad fields for debug, except PageBuddy could make trouble */
> > ===> __ClearPageBuddy(page);
> > add_taint(TAINT_BAD_PAGE);
> > }
>
> I didn't put that in for the case of the buddy allocator going wrong
> (not sure if there could be such a case - I don't mean that the buddy
> allocator is provably perfect! but how would it get here if it were
> wrong?). No, I put that in for the case when the flag bits in struct
> page have themselves got corrupted somehow, and hence we arrive at
> bad_page(): most of the bits are best left as they are, to provide
> maximum debug info; but leaving PageBuddy set there might conceivably
> allow this corrupted struct page to get paired up with its buddy later,
> and so freed for reuse, when we're trying to make sure it's never reused.

Hugh, thank you for the detailed explanations! You are always informative :)

Thanks,
Fengguang


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