Re: [Xen-devel] Need help with fixing the Xen waitqueue feature

[Olaf Hering <olaf@xxxxxxxxx>]

On Wed, Nov 23, Keir Fraser wrote:

> We have quite a big waitqueue problem actually. The current scheme of
> per-cpu stacks doesn't work nicely, as the stack pointer will change if a
> vcpu goes to sleep and then wakes up on a different cpu. This really doesn't
> work nicely with preempted C code, which may implement frame pointers and/or
> arbitrarily take the address of on-stack variables. The result will be
> hideous cross-stack corruptions, as these frame pointers and cached
> addresses of automatic variables will reference the wrong cpu's stack!
> Fixing or detecting this in general is not possible afaics.

Yes, I was thinking about that wakeup on different cpu as well.
As a quick fix/hack, perhaps the scheduler could make sure the vcpu
wakes up on the same cpu?

Olaf

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