Re: Need help with fixing the Xen waitqueue feature

[Keir Fraser <keir.xen@gmail.com>]

On 23/11/2011 18:31, "Olaf Hering" <olaf@aepfle.de> wrote:

> 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?

Could save old affinity and then vcpu_set_affinity. That will have to do for
now. Actually it should work okay as long as toolstack doesn't mess with
affinity meanwhile. I'll sort out a patch for this.

 -- Keir

> Olaf