On Thu, Sep 09, 2021 at 11:16:01AM +0200, Vasily Gorbik wrote:
> On an idle system with large amount of cpus it might happen that
> klp_update_patch_state() is not reached in do_idle() for a long periods
> of time. With debug messages enabled log is filled with:
> [ 499.442643] livepatch: klp_try_switch_task: swapper/63:0 is running
>
> without any signs of progress. Ending up with "failed to complete
> transition".
>
> On s390 LPAR with 128 cpus not a single transition is able to complete
> and livepatch kselftests fail. Tests on idling x86 kvm instance with 128
> cpus demonstrate similar symptoms with and without CONFIG_NO_HZ.
>
> To deal with that, since runqueue is already locked in
> klp_try_switch_task() identify idling cpus and trigger rescheduling
> potentially waking them up and making sure idle tasks break out of
> do_idle() inner loop and reach klp_update_patch_state(). This helps to
> speed up transition time while avoiding unnecessary extra system load.
>
> Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Looks ok to me, but we should get an ack from Ingo or Peter since
livepatch would be calling another private scheduler interface.
> ---
> Previous discussion and RFC PATCH:
> lkml.kernel.org/r/patch.git-b76842ceb035.your-ad-here.call-01625661932-ext-1304@work.hours
>
> kernel/livepatch/transition.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index 3a4beb9395c4..c5832b2dd081 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -308,6 +308,8 @@ static bool klp_try_switch_task(struct task_struct *task)
> rq = task_rq_lock(task, &flags);
>
> if (task_running(rq, task) && task != current) {
> + if (is_idle_task(task))
> + resched_curr(rq);
> snprintf(err_buf, STACK_ERR_BUF_SIZE,
> "%s: %s:%d is running\n", __func__, task->comm,
> task->pid);
> --
> 2.25.4
>
--
Josh
