[PATCH 4/6] drm/syncobj: Avoid one temporary allocation in drm_syncobj_array_find

[Tvrtko Ursulin <tursulin@xxxxxxxxxx>]

From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>

Drm_syncobj_array_find() is used from many entry points with the task of
looking up userspace handles to internal objects.

We can easily avoid one temporary allocation by making it read the handles
as it is looking them up.

"vkgears -present-mailbox" average framerate:

  Before:  21609.7225
  After:   21843.1276

With a disclaimer that measuring with vkgears feels a bit variable,
nevertheless it did not look like noise.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_syncobj.c | 44 +++++++++++++++++------------------
 1 file changed, 21 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 059d6be3ff1f..5838a7c71a76 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -1211,48 +1211,46 @@ signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec)
 EXPORT_SYMBOL(drm_timeout_abs_to_jiffies);
 
 static int drm_syncobj_array_find(struct drm_file *file_private,
-				  void __user *user_handles,
-				  uint32_t count_handles,
+				  u32 __user *handles,
+				  uint32_t count,
 				  struct drm_syncobj ***syncobjs_out)
 {
-	uint32_t i, *handles;
 	struct drm_syncobj **syncobjs;
+	uint32_t i;
 	int ret;
 
-	handles = kmalloc_array(count_handles, sizeof(*handles), GFP_KERNEL);
-	if (handles == NULL)
+	if (!access_ok(handles, count * sizeof(*handles)))
+		return -EFAULT;
+
+	syncobjs = kmalloc_array(count, sizeof(*syncobjs), GFP_KERNEL);
+	if (!syncobjs)
 		return -ENOMEM;
 
-	if (copy_from_user(handles, user_handles,
-			   sizeof(uint32_t) * count_handles)) {
-		ret = -EFAULT;
-		goto err_free_handles;
-	}
+	for (i = 0; i < count; i++) {
+		u64 handle;
 
-	syncobjs = kmalloc_array(count_handles, sizeof(*syncobjs), GFP_KERNEL);
-	if (syncobjs == NULL) {
-		ret = -ENOMEM;
-		goto err_free_handles;
-	}
-
-	for (i = 0; i < count_handles; i++) {
-		syncobjs[i] = drm_syncobj_find(file_private, handles[i]);
+		if (get_user(handle, handles++)) {
+			ret = -EFAULT;
+			syncobjs[i] = NULL;
+			goto err_put_syncobjs;
+		}
+		syncobjs[i] = drm_syncobj_find(file_private, handle);
 		if (!syncobjs[i]) {
 			ret = -ENOENT;
 			goto err_put_syncobjs;
 		}
 	}
 
-	kfree(handles);
 	*syncobjs_out = syncobjs;
 	return 0;
 
 err_put_syncobjs:
-	while (i-- > 0)
-		drm_syncobj_put(syncobjs[i]);
+	while (i > 0) {
+		if (syncobjs[i])
+			drm_syncobj_put(syncobjs[i]);
+		i--;
+	}
 	kfree(syncobjs);
-err_free_handles:
-	kfree(handles);
 
 	return ret;
 }
-- 
2.47.1