[Intel-gfx] [PATCH] drm/i915: Rely on accurate request tracking for finding hung batches

[Chris Wilson]

In the past, it was possible to have multiple batches per request due to
a stray signal or ENOMEM. As a result we had to scan each active object
(filtered by those having the COMMAND domain) for the one that contained
the ACTHD pointer. This was then made more complicated by the
introduction of ppgtt, whereby ACTHD then pointed into the address space
of the context and so also needed to be taken into account.

This is a fairly robust approach (though the implementation is a little
fragile and depends upon the per-generation setup, registers and
parameters). However, due to the requirements for hangstats, we needed a
robust method for associating batches with a particular request and
having that we can rely upon it for finding the associated batch object
for error capture.

If the batch buffer tracking is not robust enough, that should become
apparent quite quickly through an erroneous error capture. That should
also help to make sure that the runtime reporting to userspace is
robust. It also means that we then report the oldest incomplete batch on
each ring, which can be useful for determining the state of userspace at
the time of a hang.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Ben Widawsky <benjamin.widawsky at intel.com>
---
 drivers/gpu/drm/i915/i915_gpu_error.c | 59 +++++------------------------------
 1 file changed, 8 insertions(+), 51 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 96e945c3d44f..8e6d8f744e7e 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -685,46 +685,18 @@ static void i915_gem_record_fences(struct drm_device *dev,
 	}
 }
 
-/* This assumes all batchbuffers are executed from the PPGTT. It might have to
- * change in the future. */
-static bool is_active_vm(struct i915_address_space *vm,
-			 struct intel_ring_buffer *ring)
-{
-	struct drm_device *dev = vm->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct i915_hw_ppgtt *ppgtt;
-
-	if (INTEL_INFO(dev)->gen < 7)
-		return i915_is_ggtt(vm);
-
-	/* FIXME: This ignores that the global gtt vm is also on this list. */
-	ppgtt = container_of(vm, struct i915_hw_ppgtt, base);
-
-	if (INTEL_INFO(dev)->gen >= 8) {
-		u64 pdp0 = (u64)I915_READ(GEN8_RING_PDP_UDW(ring, 0)) << 32;
-		pdp0 |=  I915_READ(GEN8_RING_PDP_LDW(ring, 0));
-		return pdp0 == ppgtt->pd_dma_addr[0];
-	} else {
-		u32 pp_db;
-		pp_db = I915_READ(RING_PP_DIR_BASE(ring));
-		return (pp_db >> 10) == ppgtt->pd_offset;
-	}
-}
-
 static struct drm_i915_error_object *
 i915_error_first_batchbuffer(struct drm_i915_private *dev_priv,
 			     struct intel_ring_buffer *ring)
 {
-	struct i915_address_space *vm;
-	struct i915_vma *vma;
-	struct drm_i915_gem_object *obj;
-	bool found_active = false;
+	struct drm_i915_gem_request *request;
 	u32 seqno;
 
 	if (!ring->get_seqno)
 		return NULL;
 
 	if (HAS_BROKEN_CS_TLB(dev_priv->dev)) {
+		struct drm_i915_gem_object *obj;
 		u32 acthd = I915_READ(ACTHD);
 
 		if (WARN_ON(ring->id != RCS))
@@ -738,31 +710,16 @@ i915_error_first_batchbuffer(struct drm_i915_private *dev_priv,
 	}
 
 	seqno = ring->get_seqno(ring, false);
-	list_for_each_entry(vm, &dev_priv->vm_list, global_link) {
-		if (!is_active_vm(vm, ring))
+	list_for_each_entry(request, &ring->request_list, list) {
+		if (i915_seqno_passed(seqno, request->seqno))
 			continue;
 
-		found_active = true;
-
-		list_for_each_entry(vma, &vm->active_list, mm_list) {
-			obj = vma->obj;
-			if (obj->ring != ring)
-				continue;
-
-			if (i915_seqno_passed(seqno, obj->last_read_seqno))
-				continue;
-
-			if ((obj->base.read_domains & I915_GEM_DOMAIN_COMMAND) == 0)
-				continue;
-
-			/* We need to copy these to an anonymous buffer as the simplest
-			 * method to avoid being overwritten by userspace.
-			 */
-			return i915_error_object_create(dev_priv, obj, vm);
-		}
+		/* We need to copy these to an anonymous buffer as the simplest
+		 * method to avoid being overwritten by userspace.
+		 */
+		return i915_error_object_create(dev_priv, request->batch_obj, request->ctx->vm);
 	}
 
-	WARN_ON(!found_active);
 	return NULL;
 }
 
-- 
1.8.5.3