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SubjectRe: [patch-rt] sched,fair: Fix CFS bandwidth control lockdep DEADLOCK report
On Fri, 04 May 2018 08:14:38 +0200
Mike Galbraith <efault@gmx.de> wrote:

> CFS bandwidth control yields the inversion gripe below, moving
> handling quells it.
>
> ========================================================
> WARNING: possible irq lock inversion dependency detected
> 4.16.7-rt1-rt #2 Tainted: G E
> --------------------------------------------------------
> sirq-hrtimer/0/15 just changed the state of lock:
> (&cfs_b->lock){+...}, at: [<000000009adb5cf7>] sched_cfs_period_timer+0x28/0x140
> but this lock was taken by another, HARDIRQ-safe lock in the past:
> (&rq->lock){-...}
> and interrupts could create inverse lock ordering between them.
> other info that might help us debug this:
> Possible interrupt unsafe locking scenario:
> CPU0 CPU1
> ---- ----
> lock(&cfs_b->lock);
> local_irq_disable();
> lock(&rq->lock);
> lock(&cfs_b->lock);
> <Interrupt>
> lock(&rq->lock);
> *** DEADLOCK ***


> Signed-off-by: Mike Galbraith <efault@gmx.de>
> ---
> kernel/sched/fair.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5007,9 +5007,9 @@ void init_cfs_bandwidth(struct cfs_bandw
> cfs_b->period = ns_to_ktime(default_cfs_period());
>
> INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
> - hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
> + hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
> cfs_b->period_timer.function = sched_cfs_period_timer;
> - hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);

Looks good to me.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> cfs_b->slack_timer.function = sched_cfs_slack_timer;
> }
>

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