drm/i915: Add ww locking around vm_access()

i915_gem_object_pin_map potentially needs a ww context, so ensure we
have one we can revoke.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-35-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -421,7 +421,9 @@ vm_access(struct vm_area_struct *area, unsigned long addr,
 {
 	struct i915_mmap_offset *mmo = area->vm_private_data;
 	struct drm_i915_gem_object *obj = mmo->obj;
+	struct i915_gem_ww_ctx ww;
 	void *vaddr;
+	int err = 0;
 
 	if (i915_gem_object_is_readonly(obj) && write)
 		return -EACCES;
@@ -430,10 +432,18 @@ vm_access(struct vm_area_struct *area, unsigned long addr,
 	if (addr >= obj->base.size)
 		return -EINVAL;
 
+	i915_gem_ww_ctx_init(&ww, true);
+retry:
+	err = i915_gem_object_lock(obj, &ww);
+	if (err)
+		goto out;
+
 	/* As this is primarily for debugging, let's focus on simplicity */
 	vaddr = i915_gem_object_pin_map(obj, I915_MAP_FORCE_WC);
-	if (IS_ERR(vaddr))
-		return PTR_ERR(vaddr);
+	if (IS_ERR(vaddr)) {
+		err = PTR_ERR(vaddr);
+		goto out;
+	}
 
 	if (write) {
 		memcpy(vaddr + addr, buf, len);
@@ -443,6 +453,16 @@ vm_access(struct vm_area_struct *area, unsigned long addr,
 	}
 
 	i915_gem_object_unpin_map(obj);
+out:
+	if (err == -EDEADLK) {
+		err = i915_gem_ww_ctx_backoff(&ww);
+		if (!err)
+			goto retry;
+	}
+	i915_gem_ww_ctx_fini(&ww);
+
+	if (err)
+		return err;
 
 	return len;
 }