Re: [PATCH] [6/16] HWPOISON: Add various poison checks in mm/memory.c

Wu Fengguang
2009-06-04T04:26:19Z

On Thu, Jun 04, 2009 at 02:46:38AM +0800, Andi Kleen wrote:
>
> Bail out early when hardware poisoned pages are found in page fault handling.

I suspect this patch is also not absolutely necessary: the poisoned
page will normally have been isolated already.

> Since they are poisoned they should not be mapped freshly into processes,
> because that would cause another (potentially deadly) machine check
>
> 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 | 3 +++
> 1 file changed, 3 insertions(+)
>
> Index: linux/mm/memory.c
> ===================================================================
> --- linux.orig/mm/memory.c 2009-06-03 19:36:23.000000000 +0200
> +++ linux/mm/memory.c 2009-06-03 19:36:23.000000000 +0200
> @@ -2797,6 +2797,9 @@
> if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
> return ret;
>
> + if (unlikely(PageHWPoison(vmf.page)))
> + return VM_FAULT_HWPOISON;
> +

Direct return with locked page could lockup someone later.
Either drop this patch or fix it with this check?

Thanks,
Fengguang
---

--- linux.orig/mm/memory.c
+++ linux/mm/memory.c
@@ -2658,8 +2658,11 @@ static int __do_fault(struct mm_struct *
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
return ret;

- if (unlikely(PageHWPoison(vmf.page)))
+ if (unlikely(PageHWPoison(vmf.page))) {
+ if (ret & VM_FAULT_LOCKED)
+ unlock_page(vmf.page);
return VM_FAULT_HWPOISON;
+ }

/*
* For consistency in subsequent calls, make the faulted page always