[Intel-gfx] [RFC i-g-t] igt/gem_ringfill: Adds full ringbuffer preemption test

[Chris Wilson]

Quoting Chris Wilson (2017-08-15 23:35:46)
> end:
> For the purpose of testing, just create a debugfs that acquires
> struct_mutex on opening. Then test every ioctl and trap from a second
> client.

Whilst fun, this is focusing on the current implementation issue and
doesn't define the behaviour you want, namely that any two ioctls from
different clients for disparate resources do not block. The better test
will be setting up the typical conflicts, but playing with a
struct_mutex-blocker will show you just how widespread the immediate
problem is.
-Chris