Re: [PATCH v2 5/8] riscv_cbqri: resctrl: Add cache allocation via capacity block mask

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Traversing the global `cbqri_controllers` list without holding `cbqri_controllers_lock` during CPU hotplug risks list corruption.
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commit e1c49060a1fc98c61e36689ccda2041d360bb762
Author: Drew Fustini <fustini@kernel.org>

riscv_cbqri: resctrl: Add cache allocation via capacity block mask

This commit wires up the CBQRI capacity controllers into resctrl as
RDT_RESOURCE_L2 and RDT_RESOURCE_L3 schemata. It treats mismatched
capabilities at the same cache level as a fatal error and lazily creates
domains in the cpuhp online callback.

> diff --git a/drivers/resctrl/cbqri_resctrl.c b/drivers/resctrl/cbqri_resctrl.c
> new file mode 100644
> index 0000000000000..2f31baff032b6
> --- /dev/null
> +++ b/drivers/resctrl/cbqri_resctrl.c
[ ... ]
> +static int cbqri_attach_cpu_to_all_ctrls(unsigned int cpu)
> +{
> +	struct cbqri_controller *ctrl;
> +	int err = 0;
> +
> +	lockdep_assert_held(&cbqri_domain_list_lock);
> +
> +	list_for_each_entry(ctrl, &cbqri_controllers, list) {

[Severity: High]
Is it safe to iterate the global cbqri_controllers list without holding
cbqri_controllers_lock?

If a capacity controller is dynamically added at runtime (e.g., via a device
tree overlay instantiating the platform device), its probe function can acquire
cbqri_controllers_lock and mutate the cbqri_controllers list.

Concurrently, if a CPU is hotplugged, the cpuhp online callback calls
cbqri_resctrl_online_cpu() which invokes this function. Traversing the list
here while holding only cbqri_domain_list_lock could lead to list corruption,
resulting in an infinite loop or NULL pointer dereference.

> +		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) {
> +			cbqri_detach_cpu_from_all_ctrls(cpu);
> +			break;
> +		}
> +	}
> +
> +	return err;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260624-dfustini-atl-sc-cbqri-dt-v2-0-2f8049fd902b@kernel.org?part=5