Re: [PATCH 02/10] random: use lockless techniques when mixingentropy pools

From: Theodore Ts'o
Date: Thu Jul 05 2012 - 15:48:04 EST

On Thu, Jul 05, 2012 at 02:10:12PM -0500, Matt Mackall wrote:
> I don't think this will work correctly. It's important that simultaneous
> _readers_ of the state get different results. Otherwise, you can get
> things like duplicate UUIDs generated on different cores, something
> that's been observed in the field(!). I thought I added a comment to
> that effect some years back, but I guess not.

That's easy to fix; we just need to take a spinlock on the extract
side. The main issue is that Thomas very much doesn't want us to take
a spinlock in the interrupt handler codepath. But if we take a
spinlock while extracting, that should take care of this concern.

- Ted
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