[PATCH 2/2] drm/i915/gvt: Fix inconsistent locks holding sequence

[Chuanxiao Dong]

There are two kinds of locking sequence.

One is in the thread which is started by vfio ioctl to do
the iommu unmapping. The locking sequence is:
	down_read(&group_lock) ----> mutex_lock(&cached_lock)

The other is in the vfio release thread which will unpin all
the cached pages. The lock sequence is:
	mutex_lock(&cached_lock) ---> down_read(&group_lock)

And, the cache_lock is used to protect the rb tree of the cache
node and doing vfio unpin doesn't require this lock. Move the
vfio unpin out of the cache_lock protected region.

Fixes: f30437c5e7bf ("drm/i915/gvt: add KVMGT support")
Signed-off-by: Chuanxiao Dong <chuanxiao.dong at intel.com>
---
 drivers/gpu/drm/i915/gvt/kvmgt.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index 88a4d8f..1405c60 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -192,13 +192,6 @@ static void gvt_cache_add(struct intel_vgpu *vgpu, gfn_t gfn,
 	kfree(new);
 }
 
-static void __gvt_cache_remove_entry(struct intel_vgpu *vgpu,
-				struct gvt_dma *entry)
-{
-	rb_erase(&entry->node, &vgpu->vdev.cache);
-	kfree(entry);
-}
-
 static void intel_vgpu_unpin_work(struct work_struct *work)
 {
 	struct intel_vgpu *vgpu = container_of(work, struct intel_vgpu,
@@ -260,16 +253,22 @@ static void gvt_cache_destroy(struct intel_vgpu *vgpu)
 	struct device *dev = mdev_dev(vgpu->vdev.mdev);
 	unsigned long gfn;
 
-	mutex_lock(&vgpu->vdev.cache_lock);
-	while ((node = rb_first(&vgpu->vdev.cache))) {
+	do {
+		mutex_lock(&vgpu->vdev.cache_lock);
+		node = rb_first(&vgpu->vdev.cache);
+		if (!node) {
+			mutex_unlock(&vgpu->vdev.cache_lock);
+			break;
+		}
 		dma = rb_entry(node, struct gvt_dma, node);
 		gvt_dma_unmap_iova(vgpu, dma->iova);
-		gfn = dma->gfn;
+		rb_erase(&dma->node, &vgpu->vdev.cache);
+		mutex_unlock(&vgpu->vdev.cache_lock);
 
+		gfn = dma->gfn;
 		vfio_unpin_pages(dev, &gfn, 1);
-		__gvt_cache_remove_entry(vgpu, dma);
-	}
-	mutex_unlock(&vgpu->vdev.cache_lock);
+		kfree(dma);
+	} while (1);
 }
 
 static struct intel_vgpu_type *intel_gvt_find_vgpu_type(struct intel_gvt *gvt,
-- 
2.7.4