Date: Wed, 8 Apr 2009 11:41:59 +0200
From: Andi Kleen <andi@firstfloor.org>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, x86@kernel.org
Subject: Re: [PATCH] [3/16] POISON: Handle poisoned pages in page free
Message-ID: <20090408094159.GK17934@one.firstfloor.org>
References: <20090407509.382219156@firstfloor.org> <20090407150959.C099D1D046E@basil.firstfloor.org> <28c262360904071621j5bdd8e33u1fbd8534d177a941@mail.gmail.com> <20090408065121.GI17934@one.firstfloor.org> <28c262360904080039l65c381edn106484c88f1c5819@mail.gmail.com>
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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@firstfloor.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@linux.intel.com -- Speaking for myself only.
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