Re: [PATCH 1/2] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable()

[Sebastian Andrzej Siewior]

On 2020-10-13 15:01:15 [+0100], Valentin Schneider wrote:
>   migrate_disable();
>   set_cpus_allowed_ptr(current, {something excluding task_cpu(current)});
>   affine_move_task(); <-- never returns
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
> ---
>  kernel/sched/core.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 4ccd1099adaa..7f4e38819de1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2189,6 +2189,11 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
>  	if (!(flags & SCA_MIGRATE_ENABLE) && cpumask_equal(&p->cpus_mask, new_mask))
>  		goto out;
>  
> +	if (p == current &&
> +	    is_migration_disabled(p) &&
> +	    !cpumask_test_cpu(task_cpu(p), new_mask))
> +		ret = -EBUSY;
> +

This shouldn't happen, right? The function may sleep so it shouldn't be
entered with disabled migration. A WARN_ON might spot the bad caller.

Sebastian