On Wed 2021-07-07 14:49:38, 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
I see. I guess that the problem is only when CONFIG_NO_HZ is enabled.
Do I get it correctly, please?
> 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.
>
> To deal with that, make sure we break out of do_idle() inner loop to
> reach klp_update_patch_state() by marking idle tasks as NEED_RESCHED
> as well as kick cpus out of idle state.
>
> Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
> ---
> kernel/livepatch/transition.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index 3a4beb9395c4..793eba46e970 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -415,8 +415,11 @@ void klp_try_complete_transition(void)
> for_each_possible_cpu(cpu) {
> task = idle_task(cpu);
> if (cpu_online(cpu)) {
> - if (!klp_try_switch_task(task))
> + if (!klp_try_switch_task(task)) {
> complete = false;
> + set_tsk_need_resched(task);
> + kick_process(task);
First, we should kick the idle threads in klp_send_signals().
It already solves similar problem when normal threads and kthreads
stay in the incorruptible sleep for too long.
Second, the way looks a bit hacky to me. need_resched() depends on
the currect implementation of the idle loop. kick_process() has
a completely different purpose and does checks that do not fit well
this use-case.
I wonder if wake_up_nohz_cpu() would fit better here. Please, add
scheduler people into CC, namely:
Ingo Molnar <mingo@xxxxxxxxxx>
Peter Zijlstra <peterz@xxxxxxxxxxxxx>
and NOHZ guys:
Frederic Weisbecker <fweisbec@xxxxxxxxx>
Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Best Regards,
Petr
