Re: [PATCH v4 2/2] s390/vfio-ap: control access to PQAP(AQIC) interception handler

From: Jason Gunthorpe
Date: Tue May 25 2021 - 11:01:15 EST

On Tue, May 25, 2021 at 10:59:25AM -0400, Tony Krowiak wrote:
> > But this is alot of complicated and unused code to solve a lock
> > ordering problem..
> If you have a better solution, I'm all ears. I've been down this
> road a couple of times now and solving lock ordering for
> multiple asynchronous processes is not trivial. This seems like
> a reasonable solution and provides for flexibility for including
> additional hooks to handle interception of other AP instructions.

Lock ordering is very trivial. In this case you have to always hold
the hook lock before obtaining the matrix_dev lock. From what I
remember there was only one error on the set path where they were
ordered wrong