Re: [PATCH] [8/16] POISON: Add various poison checks in mm/memory.c

Johannes Weiner
2009-04-07T19:03:44Z

On Tue, Apr 07, 2009 at 05:10:05PM +0200, Andi Kleen wrote:
>
> Bail out early when poisoned pages are found in page fault handling.
> Since they are poisoned they should not be mapped freshly
> into processes.
>
> This is generally handled in the same way as OOM, just a different
> error code is returned to the architecture code.
>
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
>
> ---
> mm/memory.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> Index: linux/mm/memory.c
> ===================================================================
> --- linux.orig/mm/memory.c 2009-04-07 16:39:39.000000000 +0200
> +++ linux/mm/memory.c 2009-04-07 16:39:39.000000000 +0200
> @@ -2560,6 +2560,10 @@
> goto oom;
> __SetPageUptodate(page);
>
> + /* Kludge for now until we take poisoned pages out of the free lists */
> + if (unlikely(PagePoison(page)))
> + return VM_FAULT_POISON;
> +

When memory_failure() hits a page still on the free list
(!page_count()) then the get_page() in memory_failure() will trigger a
VM_BUG. So either this check is unneeded or it should be
get_page_unless_zero() in memory_failure()?