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

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Date:	Thu, 4 Jun 2009 12:26:03 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] [6/16] HWPOISON: Add various poison checks in
	mm/memory.c

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@...ux.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
--
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