[PATCH v3 8/9] kernel: export task_work_add

Desmond Cheong Zhi Xi desmondcheongzx at gmail.com
Wed Aug 18 07:38:23 UTC 2021

The task_work_add function is needed to prevent userspace races with
DRM modesetting rights.

Some DRM ioctls can change modesetting permissions while other
concurrent users are performing modesetting. To prevent races with
userspace, such functions should flush readers of old permissions
before returning to user mode. As the function that changes
permissions might itself be a reader of the old permissions, we intend
to schedule this flush using task_work_add.

However, when DRM is compiled as a loadable kernel module without
exporting task_work_add, we get the following compilation error:

ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined!

Reported-by: kernel test robot <lkp at intel.com>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx at gmail.com>
 kernel/task_work.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 1698fbe6f0e1..90000404af2b 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -60,6 +60,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 	return 0;
  * task_work_cancel_match - cancel a pending work added by task_work_add()

More information about the Linux-kernel-mentees mailing list