Re: [PATCH v6 15/16] rv: Add deadline monitors

[Juri Lelli]

Hello,

On 25/02/26 10:51, Gabriele Monaco wrote:
> Add the deadline monitors collection to validate the deadline scheduler,
> both for deadline tasks and servers.
> 
> The currently implemented monitors are:
> * throttle:
>     validate dl entities are throttled when they use up their runtime
> * nomiss:
>     validate dl entities run to completion before their deadiline
> 
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Reviewed-by: Nam Cao <namcao@xxxxxxxxxxxxx>
> Signed-off-by: Gabriele Monaco <gmonaco@xxxxxxxxxx>
> ---

...

> +static inline int extract_params(struct pt_regs *regs, long id, struct task_struct **p)
> +{
> +	size_t size = offsetof(struct sched_attr, sched_nice);
> +	struct sched_attr __user *uattr, attr;
> +	int new_policy = -1, ret;
> +	unsigned long args[6];
> +	pid_t pid;
> +
> +	switch (id) {
> +	case __NR_sched_setscheduler:
> +		syscall_get_arguments(current, regs, args);
> +		pid = args[0];
> +		new_policy = args[1];
> +		break;
> +	case __NR_sched_setattr:
> +		syscall_get_arguments(current, regs, args);
> +		pid = args[0];
> +		uattr = (void *)args[1];
> +		/*
> +		 * Just copy up to sched_flags, we are not interested after that
> +		 */
> +		ret = copy_struct_from_user(&attr, size, uattr, size);
> +		if (ret)
> +			return ret;
> +		if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
> +			return -EINVAL;
> +		new_policy = attr.sched_policy;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +	if (!pid)
> +		*p = current;
> +	else {
> +		/*
> +		 * Required for find_task_by_vpid, make sure the caller doesn't
> +		 * need to get_task_struct().
> +		 */
> +		guard(rcu)();
> +		*p = find_task_by_vpid(pid);
> +		if (unlikely(!*p))
> +			return -EINVAL;
> +	}

Not sure I get this comment. RCU is released when the function returns,
but then the task pointer is dereferenced by callers?

Thanks,
Juri