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Re: [Xen-devel] Need help with fixing the Xen waitqueue feature
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Keir Fraser <keir@xxxxxxx>
- Date: Thu, 24 Nov 2011 09:51:27 +0000
- Cc: Olaf Hering <olaf@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 24 Nov 2011 09:52:36 +0000
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- Thread-topic: [Xen-devel] Need help with fixing the Xen waitqueue feature
On 24/11/2011 09:15, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> Attached three patches for you to try. They apply in sequence.
>> 00: A fixed version of "domain_crash on stack overflow"
>> 01: Reorders prepare_to_wait so that the vcpu will always be on the
>> waitqueue on exit (even if it has just been woken).
>> 02: Ensures the vcpu wakes up on the same cpu that it slept on.
> Didn't we (long ago) settle on not permitting new calls to
> domain_crash_synchronous()? Is it really impossible to just
> domain_crash() in any of the instances these add?
It's safe because you must be in a context that is safe to preempt. That's a
pre-condition for using a waitqueue. It's not safe to use domain_crash()
because the caller of wait_event() may not handle the exceptional return.
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