Hi Tony,
On 2/28/2024 11:36 AM, Tony Luck wrote:
> reset_all_ctrls() and resctrl_arch_update_domains() use on_each_cpu_mask()
> to call rdt_ctrl_update() on potentially one CPU from each domain.
>
> But this means rdt_ctrl_update() needs to figure out which domain to
> apply changes to. Doing so requires a search of all domains in a resource,
> which can only be done safely if cpus_lock is held. Both callers do hold
> this lock, but there isn't a way for a function called on another CPU
> via IPI to verify this.
>
> Commit c0d848fcb09d ("x86/resctrl: Remove lockdep annotation that triggers
> false positive") removed the incorrect assertions.
>
> Add the target domain to the msr_param structure and
> call rdt_ctrl_update() for each domain separately using
> smp_call_function_single(). This means that rdt_ctrl_update() doesn't
> need to search for the domain and get_domain_from_cpu() can safely assert
> that the cpus_lock is held since the remaining callers do not use IPI.
>
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
...
> @@ -315,27 +300,27 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
> struct rdt_hw_domain *hw_dom;
> struct msr_param msr_param;
> enum resctrl_conf_type t;
> - cpumask_var_t cpu_mask;
> struct rdt_domain *d;
> + int cpu;
> u32 idx;
>
> /* Walking r->domains, ensure it can't race with cpuhp */
> lockdep_assert_cpus_held();
>
> - if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
> - return -ENOMEM;
> -
> - msr_param.res = NULL;
> list_for_each_entry(d, &r->domains, list) {
> hw_dom = resctrl_to_arch_dom(d);
> + msr_param.res = NULL;
> + msr_param.dom = d;
> for (t = 0; t < CDP_NUM_TYPES; t++) {
> cfg = &hw_dom->d_resctrl.staged_config[t];
> if (!cfg->have_new_ctrl)
> continue;
>
> idx = get_config_index(closid, t);
> - if (!apply_config(hw_dom, cfg, idx, cpu_mask))
> + if (cfg->new_ctrl == hw_dom->ctrl_val[idx])
> continue;
> + hw_dom->ctrl_val[idx] = cfg->new_ctrl;
> + cpu = cpumask_any(&d->cpu_mask);
>
cpu only needs to be assigned once. How about initializing cpu to
nr_cpu_ids at the same time msr_param.res and msr_param.dom is
initialized and only assign it when msr_param.res is assigned?
I think that will be more robust.
If you agree and do this then please feel free to add:
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Reinette
