Re: [PATCH] mm: poison struct page for ptlock

[Andrew Morton <akpm@osdl.org>]

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.