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

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Date:	Wed, 20 Apr 2011 07:04:18 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.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

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 ?



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