Re: [PATCH V3 04/10] sched/core: Prevent race condition between cpuset and __sched_setscheduler()

Juri Lelli
2018-02-14T10:36:46Z

Hi Mathieu,

On 13/02/18 13:32, Mathieu Poirier wrote:
> No synchronisation mechanism exist between the cpuset subsystem and calls
> to function __sched_setscheduler(). As such it is possible that new root
> domains are created on the cpuset side while a deadline acceptance test
> is carried out in __sched_setscheduler(), leading to a potential oversell
> of CPU bandwidth.
>
> By making available the cpuset_mutex to the core scheduler it is possible
> to prevent situations such as the one described above from happening.
>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---

[...]

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f727c3d0064c..0d8badcf1f0f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4176,6 +4176,13 @@ static int __sched_setscheduler(struct task_struct *p,
> }
>
> /*
> + * Make sure we don't race with the cpuset subsystem where root
> + * domains can be rebuilt or modified while operations like DL
> + * admission checks are carried out.
> + */
> + cpuset_lock();
> +
> + /*

Mmm, I'm afraid we can't do this. __sched_setscheduler might be called
from interrupt contex by normalize_rt_tasks().

Best,

- Juri