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

Eric Dumazet
2011-04-20T05:04:26Z

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 ?