Re: [RFC PATCH v2 0/4] vfio-ccw: Fix interrupt handling for HALT/CLEAR

Cornelia Huck
2020-05-26T09:55:48Z

On Wed, 13 May 2020 16:29:30 +0200
Eric Farman <farman@linux.ibm.com> wrote:

> There was some suggestion earlier about locking the FSM, but I'm not
> seeing any problems with that. Rather, what I'm noticing is that the
> flow between a synchronous START and asynchronous HALT/CLEAR have
> different impacts on the FSM state. Consider:
>
> CPU 1 CPU 2
>
> SSCH (set state=CP_PENDING)
> INTERRUPT (set state=IDLE)
> CSCH (no change in state)
> SSCH (set state=CP_PENDING)
> INTERRUPT (set state=IDLE)
> INTERRUPT (set state=IDLE)

A different question (not related to how we want to fix this): How
easily can you trigger this bug? Is this during normal testing with a
bit of I/O stress, or do you have a special test case?