netdev - Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized memory in __alloc

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Message-ID: <alpine.DEB.2.00.1104200901010.8634@router.home>
Date:	Wed, 20 Apr 2011 09:04:08 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, casteyde.christian@...e.fr,
	Vegard Nossum <vegardno@....uio.no>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized
 memory in __alloc_skb

On Wed, 20 Apr 2011, Eric Dumazet wrote:

> Le mardi 19 avril 2011 à 16:18 -0500, Christoph Lameter a écrit :
> > On Tue, 19 Apr 2011, Eric Dumazet wrote:
> >
> > > > Ugg.. Isnt there some way to indicate to kmemcheck that a speculative
> > > > access is occurring?
> > >
> > > Yes, here is a totally untested patch (only compiled here), to keep
> > > kmemcheck & cmpxchg_double together.
> >
> > Ok looks somewhat saner. Why does DEBUG_PAGEALLOC need this? Pages are
> > never freed as long as a page is frozen and a page needs to be frozen to
> > be allocated from. I dont see how we could reference a free page.
>
> We run lockless and IRQ enabled, are you sure we cannot at this point :
>
> CPU0 - Receive an IRQ
> CPU0 - Allocate this same object consume the page(s) containing this object
> CPU0 - Pass this object/memory to another cpu1
> CPU1 - Free memory and free the page(s)
> CPU0 - Return from IRQ
> CPU0 - Access now unreachable memory ?

True this can occur.