[PATCH] mmu

[Chris Wilson]

---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 35 +++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 2d4996de7331..f9b3406401af 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -164,7 +164,6 @@ static struct i915_mmu_notifier *
 i915_mmu_notifier_create(struct mm_struct *mm)
 {
 	struct i915_mmu_notifier *mn;
-	int ret;
 
 	mn = kmalloc(sizeof(*mn), GFP_KERNEL);
 	if (mn == NULL)
@@ -179,14 +178,6 @@ i915_mmu_notifier_create(struct mm_struct *mm)
 		return ERR_PTR(-ENOMEM);
 	}
 
-	 /* Protected by mmap_sem (write-lock) */
-	ret = __mmu_notifier_register(&mn->mn, mm);
-	if (ret) {
-		destroy_workqueue(mn->wq);
-		kfree(mn);
-		return ERR_PTR(ret);
-	}
-
 	return mn;
 }
 
@@ -210,23 +201,37 @@ i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
 static struct i915_mmu_notifier *
 i915_mmu_notifier_find(struct i915_mm_struct *mm)
 {
-	struct i915_mmu_notifier *mn = mm->mn;
+	struct i915_mmu_notifier *mn;
+	int err;
 
 	mn = mm->mn;
 	if (mn)
 		return mn;
 
+	mn = i915_mmu_notifier_create(mm->mm);
+	if (IS_ERR(mn))
+		return mn;
+
+	err = 0;
 	down_write(&mm->mm->mmap_sem);
 	mutex_lock(&mm->i915->mm_lock);
-	if ((mn = mm->mn) == NULL) {
-		mn = i915_mmu_notifier_create(mm->mm);
-		if (!IS_ERR(mn))
-			mm->mn = mn;
+	if (mm->mn == NULL) {
+		/* Protected by mmap_sem (write-lock) */
+		err = __mmu_notifier_register(&mn->mn, mm->mm);
+		if (!err) {
+			/* Protected by mm_lock */
+			mm->mn = fetch_and_zero(&mn);
+		}
 	}
 	mutex_unlock(&mm->i915->mm_lock);
 	up_write(&mm->mm->mmap_sem);
 
-	return mn;
+	if (mn) {
+		destroy_workqueue(mn->wq);
+		kfree(mn);
+	}
+
+	return err ? ERR_PTR(err) : mm->mn;
 }
 
 static int
-- 
2.14.2