On Thu, May 20, 2021 at 11:36:09AM -0700, Peter Oskolkov wrote:
> @@ -67,7 +137,75 @@ SYSCALL_DEFINE4(umcg_register_task, u32, api_version, u32, flags, u32, group_id,
> */
> SYSCALL_DEFINE1(umcg_unregister_task, u32, flags)
> {
> - return -ENOSYS;
> + struct umcg_task_data *utd;
> + int ret = -EINVAL;
> +
> + rcu_read_lock();
> + utd = rcu_dereference(current->umcg_task_data);
> +
> + if (!utd || flags)
> + goto out;
> +
> + task_lock(current);
> + rcu_assign_pointer(current->umcg_task_data, NULL);
> + task_unlock(current);
> +
> + ret = 0;
> +
> +out:
> + rcu_read_unlock();
> + if (!ret && utd) {
> + synchronize_rcu();
synchronize_rcu is expensive. Do we really need to call it here? Can we
use kfree_rcu?
Where is task->umcg_task_data freed when a task is destroyed?
> + kfree(utd);
> + }
> + return ret;
> +}
> +
