On Thu, Sep 23, 2021 at 03:14:48PM +0200, Petr Mladek wrote:

IMHO, this is not safe:

CPU0				CPU1

klp_check_task(A)
  if (context_tracking_state_cpu(task_cpu(task)) == CONTEXT_USER)
     goto complete;

  clear_tsk_thread_flag(task, TIF_PATCH_PENDING);

				# task switching to kernel space
				klp_update_patch_state(A)
				       if (test_and_clear_tsk_thread_flag(task,	TIF_PATCH_PENDING))
				       //false

				# calling kernel code with old task->patch_state

	task->patch_state = klp_target_state;

BANG: CPU0 sets task->patch_state when task A is already running
	kernel code on CPU1.

Why is that a problem? That is, who actually cares about
task->patch_state ? I was under the impression that state was purely for
klp itself, to track which task has observed the new state.