On Wed, Jan 15, 2020 at 09:24:28AM -0400, Jason Gunthorpe wrote:

I was interested because you are talking about allowing the read/write side
of a rw sem to be held across a return to user space/etc, which is the
same basic problem.

No it is not; allowing the lock to be held across userspace doesn't
change the owner. This is a crucial difference, PI depends on there
being a distinct owner. That said, allowing the lock to be held across
userspace still breaks PI in that it completely wrecks the ability to
analyze the critical section.