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

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Message-ID: <20090408094159.GK17934@one.firstfloor.org>
Date:	Wed, 8 Apr 2009 11:41:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, 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 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

-Andi

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