On 19/01/2021 16:20, Chris Wilson wrote:

If we enable_breadcrumbs for a request while that request is being removed from HW; we may see that the request is active as we take the ce->signal_lock and proceed to attach the request to ce->signals. However, during unsubmission after marking the request as inactive, we see that the request has not yet been added to ce->signals and so skip the removal. Pull the check during cancel_breadcrumbs under the same spinlock as enabling so that we the two tests are consistent in enable/cancel.

Otherwise, we may insert a request onto ce->signal that we expect should not be there:

intel_context_remove_breadcrumbs:488 GEM_BUG_ON(!__i915_request_is_complete(rq))

While updating, we can note that we are always called with irqs-disabled, due to the engine->active.lock being held at the single caller, and so remove the irqsave/restore.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2931 Fixes: c18636f76344 ("drm/i915: Remove requirement for holding i915_request.lock for breadcrumbs") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: Andi Shyti andi.shyti@intel.com Cc: stable@vger.kernel.org # v5.10+

---

drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c index d098fc0c14ec..34a645d6babd 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c @@ -453,16 +453,17 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq) { struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs; struct intel_context *ce = rq->context;

• unsigned long flags; bool release;

• if (!test_and_clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))

• spin_lock(&ce->signal_lock);
• if (!test_and_clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags)) {

• spin_unlock(&ce->signal_lock);
  

  return;
• }

• spin_lock_irqsave(&ce->signal_lock, flags); list_del_rcu(&rq->signal_link); release = remove_signaling_context(b, ce);
• spin_unlock_irqrestore(&ce->signal_lock, flags);

• spin_unlock(&ce->signal_lock); if (release) intel_context_put(ce);

Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com

Regards,

Tvrtko