On Mon, May 09, 2022 at 11:52:27AM -0400, Rik van Riel wrote:
> Does this look like an approach that could work?
>
> ---8<---
> sched,livepatch: call stop_one_cpu in klp_check_and_switch_task
>
> If a running task fails to transition to the new kernel live patch after the
> first attempt, use the stopper thread to preempt it during subsequent attempts
> at switching to the new kernel live patch.
>
> <INSERT EXPERIMENTAL RESULTS HERE>
It would be helpful to add more info about the original problem being
solved, and how this is supposed to fix it.
> +static int kpatch_dummy_fn(void *dummy)
s/kpatch/klp/
> +{
> + return 0;
> +}
> +
> /*
> * Try to safely switch a task to the target patch state. If it's currently
> * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
> @@ -315,6 +321,9 @@ static bool klp_try_switch_task(struct task_struct *task)
> case -EBUSY: /* klp_check_and_switch_task() */
> pr_debug("%s: %s:%d is running\n",
> __func__, task->comm, task->pid);
> + /* Preempt the task from the second KLP switch attempt. */
> + if (klp_signals_cnt)
> + stop_one_cpu(task_cpu(task), kpatch_dummy_fn, NULL);
I must be missing something, how is briefly preempting a kthread
supposed to actually transition it? Won't it likely go back to running
on the CPU before the next periodic klp_transition_work_fn() check?
--
Josh
