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

Chris Wilson
2017-03-14T15:31:24Z

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
---
drivers/gpu/drm/i915/intel_breadcrumbs.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 2a1ed6d7ad4d..60f5eae5be41 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -286,6 +286,7 @@ 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.
@@ -511,8 +512,10 @@ 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);
--
2.11.0

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