drm/i915/gem: Flush contexts on driver release

Due to i915_perf assuming that it can use the i915_gem_context reference
to protect its i915->gem.contexts.list iteration, we need to defer removal
of the context from the list until last reference to the context is put.
However, there is a risk of triggering kernel warning on contexts list not
empty at driver release time if we deleagate that task to a worker for
i915_gem_context_release_work(), unless that work is flushed first.
Unfortunately, it is not flushed on driver release.  Fix it.

Instead of additionally calling flush_workqueue(), either directly or via
a new dedicated wrapper around it, replace last call to
i915_gem_drain_freed_objects() with existing i915_gem_drain_workqueue()
that performs both tasks.

Fixes: 75eefd8 ("drm/i915: Release i915_gem_context from a worker")
Suggested-by: Chris Wilson <[email protected]>
Signed-off-by: Janusz Krzysztofik <[email protected]>
Reviewed-by: Andi Shyti <[email protected]>
Cc: [email protected] # v5.16+
Signed-off-by: Andi Shyti <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 1cec344)
Signed-off-by: Rodrigo Vivi <[email protected]>

drivers/gpu/drm/i915/i915_gem.c

@@ -1191,7 +1191,8 @@ void i915_gem_driver_release(struct drm_i915_private *dev_priv)
 
  intel_uc_cleanup_firmwares(&to_gt(dev_priv)->uc);
 
- i915_gem_drain_freed_objects(dev_priv);
+ /* Flush any outstanding work, including i915_gem_context.release_work. */
+ i915_gem_drain_workqueue(dev_priv);
 
  drm_WARN_ON(&dev_priv->drm, !list_empty(&dev_priv->gem.contexts.list));
 }