drm/i915: Reorder struct_mutex-vs-reset_lock in i915_gem_fault()

Annoyingly, struct_mutex was not entirely eliminated from the reset
pathway; for reasons of its own, intel_display_resume() requires
struct_mutex to prepare the planes it already captured. To avoid the
immediate problem of a deadlock between the struct_mutex and the reset
srcu, we have to acquire the reset_lock before struct_mutex in
i915_gem_fault(). Now any wait underneath struct_mutex will result us in
having to forcibly reset all inflight rendering, less than ideal, but
better than a deadlock (and will do for the short term).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190221102924.13442-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -1834,9 +1834,15 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
 
 	wakeref = intel_runtime_pm_get(dev_priv);
 
+	srcu = i915_reset_trylock(dev_priv);
+	if (srcu < 0) {
+		ret = srcu;
+		goto err_rpm;
+	}
+
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)
-		goto err_rpm;
+		goto err_reset;
 
 	/* Access to snoopable pages through the GTT is incoherent. */
 	if (obj->cache_level != I915_CACHE_NONE && !HAS_LLC(dev_priv)) {
@@ -1885,12 +1891,6 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
 	if (ret)
 		goto err_unpin;
 
-	srcu = i915_reset_trylock(dev_priv);
-	if (srcu < 0) {
-		ret = srcu;
-		goto err_fence;
-	}
-
 	/* Finally, remap it using the new GTT offset */
 	ret = remap_io_mapping(area,
 			       area->vm_start + (vma->ggtt_view.partial.offset << PAGE_SHIFT),
@@ -1898,7 +1898,7 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
 			       min_t(u64, vma->size, area->vm_end - area->vm_start),
 			       &ggtt->iomap);
 	if (ret)
-		goto err_reset;
+		goto err_fence;
 
 	/* Mark as being mmapped into userspace for later revocation */
 	assert_rpm_wakelock_held(dev_priv);
@@ -1908,14 +1908,14 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
 
 	i915_vma_set_ggtt_write(vma);
 
-err_reset:
-	i915_reset_unlock(dev_priv, srcu);
 err_fence:
 	i915_vma_unpin_fence(vma);
 err_unpin:
 	__i915_vma_unpin(vma);
 err_unlock:
 	mutex_unlock(&dev->struct_mutex);
+err_reset:
+	i915_reset_unlock(dev_priv, srcu);
 err_rpm:
 	intel_runtime_pm_put(dev_priv, wakeref);
 	i915_gem_object_unpin_pages(obj);