Re: printk deadlock due to double lock attempt on current CPU's runqueue

Vincent Guittot
2021-11-12T07:51:29Z

On Wed, 10 Nov 2021 at 20:50, Sultan Alsawaf <sultan@kerneltoast.com> wrote:
>
> On Wed, Nov 10, 2021 at 10:00:35AM +0100, Vincent Guittot wrote:
> > Is it the same SCHED_WARN_ON(rq->tmp_alone_branch !=
> > &rq->leaf_cfs_rq_list); that generates the deadlock on v5.15 too ?
> >
> > one remaining tmp_alone_branch warning has been fixed in v5.15 with
> > 2630cde26711 ("sched/fair: Add ancestors of unthrottled undecayed cfs_rq")
>
> I should clarify that I didn't actually reproduce the issue on v5.15; I just saw
> that the call chain leading to the deadlock still existed in v5.15 after looking
> through the code.

Thanks for the clarification

>
> Failing the SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list); assert
> is extremely rare in my experience, and I don't have a reproducer. It has only
> happened once after months of heavy usage (with lots of reboots too, so not with
> crazy high uptime).
>
> Sultan