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SubjectRe: [PATCH] mm: poison struct page for ptlock
Andrew Morton <akpm@osdl.org> wrote:
>
> Hugh Dickins <hugh@veritas.com> wrote:
> >
> > The split ptlock patch enlarged the default SMP PREEMPT struct page from
> > 32 to 36 bytes on most 32-bit platforms, from 32 to 44 bytes on PA-RISC
> > 7xxx (without PREEMPT). That was not my intention, and I don't believe
> > that split ptlock deserves any such slice of the user's memory.
> >
> > While leaving most of the page_private() mods in place for the moment,
> > could we please try this patch, or something like it? Again to overlay
> > the spinlock_t from &page->private onwards, with corrected BUILD_BUG_ON
> > that we don't go beyond ->lru; with poisoning of the fields overlaid,
> > and unsplit config verifying that the split config is safe to use them.
> >
>
> This patch makes the ppc64 crash. See
> http://www.zip.com.au/~akpm/linux/patches/stuff/dsc02976.jpg
>
> I don't know what the access address was (ia32 nicely tells you), but if
> it's `DAR' then we have LIST_POISON1. Which would indicate that the slab
> page which backs the mm_struct itself is getting freed-up-pte-page
> treatment, which is deeply screwed up.
>
> I'll try it on x86_64 and ia64, see if it's specific to ppc64.

Yup, the patch works OK on x86, x86_64 and ia64.
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