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drm/i915: relative_constants_mode race fix

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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: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Keith Packard <keithp@keithp.com>
This commit is contained in:
Ben Widawsky 2011-12-12 19:21:57 -08:00 committed by Keith Packard
parent 7a7e8734ac
commit e2971bdab2
1 changed files with 16 additions and 13 deletions
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29
drivers/gpu/drm/i915/i915_gem_execbuffer.c
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@ -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;