[PATCH] drm/i915: fix use-after-free in i915_drop_caches_set

[Michel Thierry <michel.thierry@intel.com>]

With the new vma/ppgtt lifetime rules, the ppgtt (vm) could be removed
after i915_vma_unbind.

Use list_for_each_entry_safe() to prevent this use-after-free.

Found with gem_persistent_relocs and gem_evict_everything igt tests.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index dd736c0..4b05cd8 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -3820,8 +3820,8 @@ i915_drop_caches_set(void *data, u64 val)
 	struct drm_device *dev = data;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj, *next;
-	struct i915_address_space *vm;
-	struct i915_vma *vma, *x;
+	struct i915_address_space *vm, *x;
+	struct i915_vma *vma, *y;
 	int ret;
 
 	DRM_DEBUG("Dropping caches: 0x%08llx\n", val);
@@ -3842,8 +3842,9 @@ i915_drop_caches_set(void *data, u64 val)
 		i915_gem_retire_requests(dev);
 
 	if (val & DROP_BOUND) {
-		list_for_each_entry(vm, &dev_priv->vm_list, global_link) {
-			list_for_each_entry_safe(vma, x, &vm->inactive_list,
+		list_for_each_entry_safe(vm, x, &dev_priv->vm_list,
+				global_link) {
+			list_for_each_entry_safe(vma, y, &vm->inactive_list,
 						 mm_list) {
 				if (vma->pin_count)
 					continue;
-- 
2.0.3