drm/i915/breadcrumbs: Assert that we do not shortcut the current bottom-half

We need to ensure that we always serialize updates to the bottom-half
using the breadcrumbs.irq_lock so that we don't race with a concurrent
interrupt handler. This is most important just prior to leaving the
waiter (when the intel_wait will be overwritten), so make sure we are
not the current bottom-half when skipping the irq locks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170315210726.12095-4-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index e2dbd91..cb6985a 100644 (file)
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -287,6 +287,7 @@ static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
                                              struct intel_wait *wait)
 {
        lockdep_assert_held(&b->rb_lock);
+       GEM_BUG_ON(b->irq_wait == wait);
 
        /* This request is completed, so remove it from the tree, mark it as
         * complete, and *then* wake up the associated task.
@@ -512,8 +513,10 @@ void intel_engine_remove_wait(struct intel_engine_cs *engine,
         * the tree by the bottom-half to avoid contention on the spinlock
         * by the herd.
         */
-       if (RB_EMPTY_NODE(&wait->node))
+       if (RB_EMPTY_NODE(&wait->node)) {
+               GEM_BUG_ON(READ_ONCE(b->irq_wait) == wait);
                return;
+       }
 
        spin_lock_irq(&b->rb_lock);
        __intel_engine_remove_wait(engine, wait);