Re: [PATCH -next] arch_topology: Fix cache attributes detection in the CPU hotplug path

Ionela Voinescu
2022-07-14T17:52:55Z

Hi Sudeep,

Thank you for the fix!

On Wednesday 13 Jul 2022 at 14:33:44 (+0100), Sudeep Holla wrote:
> init_cpu_topology() is called only once at the boot and all the cache
> attributes are detected early for all the possible CPUs. However when
> the CPUs are hotplugged out, the cacheinfo gets removed. While the
> attributes are added back when the CPUs are hotplugged back in as part
> of CPU hotplug state machine, it ends up called quite late after the
> update_siblings_masks() are called in the secondary_start_kernel()
> resulting in wrong llc_sibling_masks.
>
> Move the call to detect_cache_attributes() inside update_siblings_masks()
> to ensure the cacheinfo is updated before the LLC sibling masks are
> updated. This will fix the incorrect LLC sibling masks generated when
> the CPUs are hotplugged out and hotplugged back in again.
>
> Reported-by: Ionela Voinescu <ionela.voinescu@arm.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
> drivers/base/arch_topology.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> Hi Conor,
>
> Ionela reported an issue with the CPU hotplug and as a fix I need to
> move the call to detect_cache_attributes() which I had thought to keep
> it there from first but for no reason had moved it to init_cpu_topology().
>
> Wonder if this fixes the -ENOMEM on RISC-V as this one is called on the
> cpu in the secondary CPUs init path while init_cpu_topology executed
> detect_cache_attributes() for all possible CPUs much earlier. I think
> this might help as the percpu memory might be initialised in this case.
>
> Anyways give this a try, also test the CPU hotplug and check if nothing
> is broken on RISC-V. We noticed this bug only on one platform while
>
> Regards,
> Sudeep
>
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 441e14ac33a4..0424b59b695e 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -732,7 +732,11 @@ const struct cpumask *cpu_clustergroup_mask(int cpu)
> void update_siblings_masks(unsigned int cpuid)
> {
> struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
> - int cpu;
> + int cpu, ret;
> +
> + ret = detect_cache_attributes(cpuid);
> + if (ret)
> + pr_info("Early cacheinfo failed, ret = %d\n", ret);
> /* update core and thread sibling masks */
> for_each_online_cpu(cpu) {
> @@ -821,7 +825,7 @@ __weak int __init parse_acpi_topology(void)
> #if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
> void __init init_cpu_topology(void)
> {
> - int ret, cpu;
> + int ret;
> reset_cpu_topology();
> ret = parse_acpi_topology();
> @@ -836,13 +840,5 @@ void __init init_cpu_topology(void)
> reset_cpu_topology();
> return;
> }
> -
> - for_each_possible_cpu(cpu) {
> - ret = detect_cache_attributes(cpu);
> - if (ret) {
> - pr_info("Early cacheinfo failed, ret = %d\n", ret);
> - break;
> - }
> - }
> }
> #endif
> --2.37.1
>

Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>
Tested-by: Ionela Voinescu <ionela.voinescu@arm.com>

Kind regards,
Ionela.