[Intel-gfx] [PATCH 02/37] drm/i915/gt: Protect context lifetime with RCU

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-08-05 16:03:58)
> 
> On 05/08/2020 13:21, Chris Wilson wrote:
> > Allow a brief period for continued access to a dead intel_context by
> > deferring the release of the struct until after an RCU grace period.
> > As we are using a dedicated slab cache for the contexts, we can defer
> > the release of the slab pages via RCU, with the caveat that individual
> > structs may be reused from the freelist within an RCU grace period. To
> > handle that, we have to avoid clearing members of the zombie struct.
> 
> Is this related to debugfs race, optimising the driver latencies or 
> both? Need to hack up mutex_reinit bothers me, on top of general desire 
> to avoid even more rcu complexity.

There's an issue in the next patch exposed by virtual engine
destruction that needs a fix handily provided by the rcu grace period,
and it's used in the following patch to reduce irqoff lock contention.
-Chris