linux-kernel - Re: [PATCH v20 14/18] x86/resctrl: Fill out rmid_read structure for smp

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Date: Thu, 20 Jun 2024 14:31:13 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
	"Maciej Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v20 14/18] x86/resctrl: Fill out rmid_read structure for
 smp_call*() to read a counter

Hi Tony,

On 6/10/24 11:35 AM, Tony Luck wrote:
> mon_event_read() fills out most fields of the struct rmid_read that is
> passed via an smp_call*() function to a CPU that is part of the correct
> domain to read the monitor counters.
> 
> With Sub-NUMA Cluster (SNC) mode there are now two cases to handle:
> 
> 1) Reading a file that returns a value for a single domain.
>     + Choose the CPU to execute from the domain cpu_mask
> 
> 2) Reading a file that must sum across domains sharing an L3 cache
>     instance.
>     + Indicate to called code that a sum is needed by passing a NULL
>       rdt_mon_domain pointer.
>     + Choose the CPU from the L3 shared_cpu_map.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>

The kerneldoc in patch #9 introduces new requirements related to
struct rmid_read wrt how NULL values are interpreted and
used. This makes it essential that struct rmid_read is always initialized
correctly and should no longer consist of whatever is on the stack. I
mentioned in response to v19 that static checkers found issues here.
I understand that mbm_update() always sets the domain in
struct rmid_read, but I do not find it acceptable that it
passes garbage as the cacheinfo pointer based on subtle assumptions on
when/how __mon_event_count() uses this field.

> ---
>   arch/x86/kernel/cpu/resctrl/internal.h    |  2 +-
>   arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 39 ++++++++++++++++++-----
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c    |  2 +-
>   3 files changed, 33 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 77da29ced7eb..75bb1afc4842 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -627,7 +627,7 @@ void mon_event_count(void *info);
>   int rdtgroup_mondata_show(struct seq_file *m, void *arg);
>   void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>   		    struct rdt_mon_domain *d, struct rdtgroup *rdtgrp,
> -		    int evtid, int first);
> +		    cpumask_t *cpumask, int evtid, int first);
>   void mbm_setup_overflow_handler(struct rdt_mon_domain *dom,
>   				unsigned long delay_ms,
>   				int exclude_cpu);
> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> index 3b9383612c35..5a43931fd423 100644
> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
> @@ -515,7 +515,7 @@ static int smp_mon_event_count(void *arg)
>   
>   void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>   		    struct rdt_mon_domain *d, struct rdtgroup *rdtgrp,
> -		    int evtid, int first)
> +		    cpumask_t *cpumask, int evtid, int first)
>   {
>   	int cpu;
>   
> @@ -537,7 +537,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>   		return;
>   	}
>   
> -	cpu = cpumask_any_housekeeping(&d->hdr.cpu_mask, RESCTRL_PICK_ANY_CPU);
> +	cpu = cpumask_any_housekeeping(cpumask, RESCTRL_PICK_ANY_CPU);
>   
>   	/*
>   	 * cpumask_any_housekeeping() prefers housekeeping CPUs, but
> @@ -546,7 +546,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>   	 * counters on some platforms if its called in IRQ context.
>   	 */
>   	if (tick_nohz_full_cpu(cpu))
> -		smp_call_function_any(&d->hdr.cpu_mask, mon_event_count, rr, 1);
> +		smp_call_function_any(cpumask, mon_event_count, rr, 1);
>   	else
>   		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
>   
> @@ -575,16 +575,39 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>   	resid = md.u.rid;
>   	domid = md.u.domid;
>   	evtid = md.u.evtid;
> -
>   	r = &rdt_resources_all[resid].r_resctrl;
> -	hdr = rdt_find_domain(&r->mon_domains, domid, NULL);
> -	if (!hdr || WARN_ON_ONCE(hdr->type != RESCTRL_MON_DOMAIN)) {
> +
> +	if (md.u.sum) {
> +		/*
> +		 * This file requires summing across all SNC domains that share
> +		 * the L3 cache id that was provided in the "domid" field of the
> +		 * mon_data_bits union. Search all domains in the resource for
> +		 * one that matches this cache id.
> +		 */
> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
> +			if (d->ci->id == domid) {
> +				rr.ci = d->ci;
> +				mon_event_read(&rr, r, NULL, rdtgrp, &d->ci->shared_cpu_map, evtid, false);

Please split this line, it is over 100

Reinette