Re: Xen PVM: Strange lockups when running PostgreSQL load

[Stefan Bader <stefan.bader@canonical.com>]

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On 18.10.2012 09:08, Jan Beulich wrote:
>>>> On 18.10.12 at 09:00, "Jan Beulich" <JBeulich@suse.com> wrote:
>>>>> On 17.10.12 at 17:35, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>>> In each case, the event channels are masked (no surprise given the
>>> conversation so far on this thread), and have no pending events. 
>>> Therefore, I believe we are looking at the same bug.
>>
>> That seems very unlikely (albeit not impossible) to me, given that
>> the non-pvops kernel uses ticket locks while the pvops one doesn't.
> 
> And in fact we had a similar problem with our original ticket lock
> implementation, exposed by an open coded lock in the scheduler's
> run queue management. But that was really ticket lock specific,
> in that the fact that a CPU could passively become the owner of
> a lock while polling - that's impossible with pvops' byte locks afaict.

One of the trains of thought I had was whether it could happen that a cpu is in
polling and the task gets moved. But I don't think it can happen as the
hypercall unlikely is a place where any schedule happens (preempt is none). And
it would be much more common...

One detail which I hope someone can fill in is the whole "interrupted spinlock"
thing. Saving the last lock pointer stored on the per-cpu lock_spinners and so
on. Is that really only for spinlocks taken without interrupts disabled or do I
miss something there?




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