Re: [PATCH v3 10/19] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep

From: Reinette Chatre <reinette.chatre@intel.com>
To: James Morse <james.morse@arm.com>, <x86@kernel.org>,
	<linux-kernel@vger.kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	H Peter Anvin <hpa@zytor.com>, Babu Moger <Babu.Moger@amd.com>,
	<shameerali.kolothum.thodi@huawei.com>,
	D Scott Phillips OS <scott@os.amperecomputing.com>,
	<carl@os.amperecomputing.com>, <lcherian@marvell.com>,
	<bobo.shaobowang@huawei.com>, <tan.shaopeng@fujitsu.com>,
	<xingxin.hx@openanolis.org>, <baolin.wang@linux.alibaba.com>,
	Jamie Iles <quic_jiles@quicinc.com>,
	Xin Hao <xhao@linux.alibaba.com>, <peternewman@google.com>
Subject: Re: [PATCH v3 10/19] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep
Date: Fri, 31 Mar 2023 16:26:11 -0700	[thread overview]
Message-ID: <db59f6df-feb0-280d-88bd-6bbf1b6e7a1e@intel.com> (raw)
In-Reply-To: <20230320172620.18254-11-james.morse@arm.com>

Hi James,

On 3/20/2023 10:26 AM, James Morse wrote:

...

>  int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
>  			   u32 closid, u32 rmid, enum resctrl_event_id eventid,
>  			   u64 *val)
>  {
>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>  	struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
> +	struct __rmid_read_arg arg;
>  	struct arch_mbm_state *am;
>  	u64 msr_val, chunks;
> -	int ret;
> +	int err;
>  
> -	if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
> -		return -EINVAL;
> +	arg.rmid = rmid;
> +	arg.eventid = eventid;
>  
> -	ret = __rmid_read(rmid, eventid, &msr_val);
> -	if (ret)
> -		return ret;
> +	err = smp_call_function_any(&d->cpu_mask, smp_call_rmid_read, &arg, true);
> +	if (err)
> +		return err;

This seems to break the assumption of expected return values. __mon_event_count()
does: 
	rr->err = resctrl_arch_rmid_read()

and later rdtgroup_mondata_show() only expects -EIO or -EINVAL as errors, with
default of success.

> +	if (arg.err)
> +		return arg.err;
> +	msr_val = arg.msr_val;
>  

Reinette