Re: [PATCH RFC v5 11/18] riscv_cbqri: resctrl: Add cache allocation via capacity block mask

[Drew Fustini <fustini@kernel.org>]

On Mon, May 25, 2026 at 12:50:55AM +0000, sashiko-bot@kernel.org wrote:
> > @@ -595,6 +595,7 @@ config RISCV_ISA_SSQOSID
> >  	bool "Ssqosid extension support for supervisor mode Quality of Service ID"
> >  	depends on 64BIT
> >  	default n
> > +	select ARCH_HAS_CPU_RESCTRL
> 
> [Severity: High]
> Could this lead to build failures if the CBQRI driver is not enabled?
> 
> The Kconfig symbol RISCV_ISA_SSQOSID unconditionally selects
> ARCH_HAS_CPU_RESCTRL, which signals to the core kernel that the architecture
> provides the resctrl_arch_* interface. This permits CONFIG_RESCTRL_FS to be
> enabled.
> 
> However, since the implementation resides in drivers/resctrl/cbqri_resctrl.c
> which is only compiled when CONFIG_RISCV_CBQRI_DRIVER is set, enabling
> RISCV_ISA_SSQOSID and RESCTRL_FS without RISCV_CBQRI_DRIVER might cause
> linker errors due to undefined references to the resctrl_arch_* functions.
> Would it be safer to add a dependency on the driver?

The combination of SSQOSID=y RESCTRL_FS=y RISCV_CBQRI_DRIVER=n should
not be reachable.

> > +static int cbqri_resctrl_online_cpu(unsigned int cpu)
> > +{
> > +	struct cbqri_controller *ctrl;
> > +	int err = 0;
> > +
> > +	mutex_lock(&cbqri_domain_list_lock);
> > +
> > +	list_for_each_entry(ctrl, &cbqri_controllers, list) {
> > +		if (ctrl->type != CBQRI_CONTROLLER_TYPE_CAPACITY)
> > +			continue;
> > +		if (!cpumask_test_cpu(cpu, &ctrl->cache.cpu_mask))
> > +			continue;
> > +		if (!ctrl->alloc_capable)
> > +			continue;
> > +
> > +		err = cbqri_attach_cpu_to_cap_ctrl(ctrl, cpu);
> > +		if (err)
> > +			break;
> > +	}
> 
> [Severity: High]
> Does this loop leave the system in an inconsistent state if it fails partway
> through?

Yes, I will update v6 to track the last successfully attached controller
and walk the list backwards from there on error.

> Should we reset the per-CPU default closid and rmid when a CPU comes online?
>
> Does this missing notification leave the generic resctrl subsystem out of sync?

Yes to both. I will make v6 follow the same approach of x86
resctrl_arch_online_cpu().

Drew