drm/radeon: fix vm deadlocks on cayman

commit bb409155 upstream.

Locking mutex in different orders just screams for
deadlocks, and some testing showed that it is actually
quite easy to trigger them.
Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/radeon/radeon_gart.c

@@ -478,12 +478,18 @@ int radeon_vm_bo_add(struct radeon_device *rdev,
 
 	mutex_lock(&vm->mutex);
 	if (last_pfn > vm->last_pfn) {
-		/* grow va space 32M by 32M */
-		unsigned align = ((32 << 20) >> 12) - 1;
+		/* release mutex and lock in right order */
+		mutex_unlock(&vm->mutex);
 		radeon_mutex_lock(&rdev->cs_mutex);
-		radeon_vm_unbind_locked(rdev, vm);
+		mutex_lock(&vm->mutex);
+		/* and check again */
+		if (last_pfn > vm->last_pfn) {
+			/* grow va space 32M by 32M */
+			unsigned align = ((32 << 20) >> 12) - 1;
+			radeon_vm_unbind_locked(rdev, vm);
+			vm->last_pfn = (last_pfn + align) & ~align;
+		}
 		radeon_mutex_unlock(&rdev->cs_mutex);
-		vm->last_pfn = (last_pfn + align) & ~align;
 	}
 	head = &vm->va;
 	last_offset = 0;
@@ -597,8 +603,8 @@ int radeon_vm_bo_rmv(struct radeon_device *rdev,
 	if (bo_va == NULL)
 		return 0;
 
-	mutex_lock(&vm->mutex);
 	radeon_mutex_lock(&rdev->cs_mutex);
+	mutex_lock(&vm->mutex);
 	radeon_vm_bo_update_pte(rdev, vm, bo, NULL);
 	radeon_mutex_unlock(&rdev->cs_mutex);
 	list_del(&bo_va->vm_list);
@@ -643,9 +649,8 @@ void radeon_vm_fini(struct radeon_device *rdev, struct radeon_vm *vm)
 	struct radeon_bo_va *bo_va, *tmp;
 	int r;
 
-	mutex_lock(&vm->mutex);
-
 	radeon_mutex_lock(&rdev->cs_mutex);
+	mutex_lock(&vm->mutex);
 	radeon_vm_unbind_locked(rdev, vm);
 	radeon_mutex_unlock(&rdev->cs_mutex);