linux-kernel - Re: [PATCH] [3/16] POISON: Handle poisoned pages in page free

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Date:	Wed, 8 Apr 2009 19:05:30 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH] [3/16] POISON: Handle poisoned pages in page free

On Wed, Apr 8, 2009 at 6:41 PM, Andi Kleen <andi@...stfloor.org> wrote:
> On Wed, Apr 08, 2009 at 04:39:17PM +0900, Minchan Kim wrote:
>> On Wed, Apr 8, 2009 at 3:51 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> >> >
>> >> >        /*
>> >> > +        * Page may have been marked bad before process is freeing it.
>> >> > +        * Make sure it is not put back into the free page lists.
>> >> > +        */
>> >> > +       if (PagePoison(page)) {
>> >> > +               /* check more flags here... */
>> >>
>> >> How about adding WARNING with some information(ex, pfn, flags..).
>> >
>> > The memory_failure() code is already quite chatty. Don't think more
>> > noise is needed currently.
>>
>> Sure.
>>
>> > Or are you worrying about the case where a page gets corrupted
>> > by software and suddenly has Poison bits set? (e.g. 0xff everywhere).
>> > That would deserve a printk, but I'm not sure how to reliably test for
>> > that. After all a lot of flag combinations are valid.
>>
>> I misunderstood your code.
>> That's because you add the code in bad_page.
>>
>> As you commented, your intention was to prevent bad page from returning buddy.
>> Is right ?
>
> Yes. Well actually it should not happen anymore. Perhaps I should
> make it a BUG()
>
>> If it is right, how about adding prevention code to free_pages_check ?
>> Now, bad_page is for showing the information that why it is bad page
>> I don't like emergency exit in bad_page.
>
> There's already one in there, so i just reused that one. It was a convenient
> way to keep things out of the fast path


Sorry for my vague previous comment.
I mean bad_page function's role is just to print why it is bad now.
Whoever can use bad_page to show information.
If someone begin to add side branch in bad_page, anonther people might
add his exception case in one.

So, I think it would be better to check PagePoison in free_pages_check
not bad_page. :)

> -Andi
>
> ak@...ux.intel.com -- Speaking for myself only.
>



-- 
Kinds regards,
Minchan Kim
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