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Commit e2971bda authored by Ben Widawsky's avatar Ben Widawsky Committed by Keith Packard
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drm/i915: relative_constants_mode race fix 



dev_priv keeps track of the current addressing mode that gets set at
execbuffer time. Unfortunately the existing code was doing this before
acquiring struct_mutex which leaves a race with another thread also
doing an execbuffer. If that wasn't bad enough, relocate_slow drops
struct_mutex which opens a much more likely error where another thread
comes in and modifies the state while relocate_slow is being slow.

The solution here is to just defer setting this state until we
absolutely need it, and we know we'll have struct_mutex for the
remainder of our code path.

v2: Keith noticed a bug in the original patch.

Signed-off-by: default avatarBen Widawsky <ben@bwidawsk.net>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: default avatarKeith Packard <keithp@keithp.com>
parent 7a7e8734

drivers/gpu/drm/i915/i915_gem_execbuffer.c

+16 −13
Original line number Diff line number Diff line
@@ -1033,19 +1033,6 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data, 
			if (INTEL_INFO(dev)->gen > 5 &&

			    mode == I915_EXEC_CONSTANTS_REL_SURFACE)

				return -EINVAL;



			ret = intel_ring_begin(ring, 4);

			if (ret)

				return ret;



			intel_ring_emit(ring, MI_NOOP);

			intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(1));

			intel_ring_emit(ring, INSTPM);

			intel_ring_emit(ring,

					I915_EXEC_CONSTANTS_MASK << 16 | mode);

			intel_ring_advance(ring);



			dev_priv->relative_constants_mode = mode;

		}

		break;

	default:
@@ -1176,6 +1163,22 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data, 
		}

	}



	if (ring == &dev_priv->ring[RCS] &&

	    mode != dev_priv->relative_constants_mode) {

		ret = intel_ring_begin(ring, 4);

		if (ret)

				goto err;



		intel_ring_emit(ring, MI_NOOP);

		intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(1));

		intel_ring_emit(ring, INSTPM);

		intel_ring_emit(ring,

				I915_EXEC_CONSTANTS_MASK << 16 | mode);

		intel_ring_advance(ring);



		dev_priv->relative_constants_mode = mode;

	}



	trace_i915_gem_ring_dispatch(ring, seqno);



	exec_start = batch_obj->gtt_offset + args->batch_start_offset;