linux-kernel - Re: [RFC PATCH 5/6] sched/isolation: Make HK_FLAG

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Message-ID: <20210721142726.GA206211@e120877-lin.cambridge.arm.com>
Date:   Wed, 21 Jul 2021 15:28:45 +0100
From:   Vincent Donnefort <vincent.donnefort@....com>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        Nitesh Lal <nilal@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Saenz <nsaenzju@...hat.com>,
        Christoph Lameter <cl@...two.de>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH 5/6] sched/isolation: Make HK_FLAG_DOMAIN mutable

Hi Frederic,

[...]

>  
> +// Only support HK_FLAG_DOMAIN for now
> +// TODO: propagate the changes through all interested subsystems:
> +// workqueues, net, pci; ...
> +void housekeeping_cpumask_set(struct cpumask *mask, enum hk_flags flags)
> +{
> +	/* Only HK_FLAG_DOMAIN change supported for now */
> +	if (WARN_ON_ONCE(flags != HK_FLAG_DOMAIN))
> +		return;
>  
> +	if (!static_key_enabled(&housekeeping_overridden.key)) {
> +		if (cpumask_equal(mask, cpu_possible_mask))
> +			return;
> +		if (WARN_ON_ONCE(!alloc_cpumask_var(&hk_domain_mask, GFP_KERNEL)))
> +			return;
> +		cpumask_copy(hk_domain_mask, mask);
> +		static_branch_enable(&housekeeping_overridden);

I get a warning here. static_branch_enable() is trying to take cpus_read_lock().
But the same lock is already taken by cpuset_write_u64().

Also, shouldn't it set HK_FLAG_DOMAIN in housekeeping_flags to enable
housekeeping if the kernel started without isolcpus="" ?

-- 
Vincent