Re: [PATCH 3/6] sched,perf,kvm: Fix preemption condition

Peter Zijlstra
2021-06-02T14:16:52Z

On Wed, Jun 02, 2021 at 09:59:07AM -0400, Mathieu Desnoyers wrote:
> ----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz@infradead.org wrote:
>
> > When ran from the sched-out path (preempt_notifier or perf_event),
> > p->state is irrelevant to determine preemption. You can get preempted
> > with !task_is_running() just fine.
> >
> > The right indicator for preemption is if the task is still on the
> > runqueue in the sched-out path.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > kernel/events/core.c | 7 +++----
> > virt/kvm/kvm_main.c | 2 +-
> > 2 files changed, 4 insertions(+), 5 deletions(-)
> >
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -8568,13 +8568,12 @@ static void perf_event_switch(struct tas
> > },
> > };
> >
> > - if (!sched_in && task->state == TASK_RUNNING)
> > + if (!sched_in && current->on_rq) {
>
> This changes from checking task->state to current->on_rq, but this change
> from "task" to "current" is not described in the commit message, which is odd.
>
> Are we really sure that task == current here ?

Yeah, @task == @prev == current at this point, but yes, not sure why I
changed that... lemme change that back to task.