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

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Message-ID: <1305057989.2437.18.camel@edumazet-laptop>
Date:	Tue, 10 May 2011 22:06:29 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Vegard Nossum <vegardno@....uio.no>,
	Pekka Enberg <penberg@...helsinki.fi>,
	casteyde.christian@...e.fr,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from
 uninitialized memory in __alloc_skb

Le mardi 10 mai 2011 à 14:38 -0500, Christoph Lameter a écrit :

> Optimizing? You think about this as concurrency issue between multiple
> cpus. That is fundamentally wrong. This is dealing with access to per cpu
> data and the concurrency issues are only with code running on the *same*
> cpu.
> 

If you enable irqs, then this object can be allocated by _this_ cpu and
given to another one.

Another cpu can free the page, forcing you to call a very expensive
function, that might give obsolete result as soon it returns.

Maybe I am just tired tonight, this seems very obvious, I must miss
something.



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