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

[Greg Kroah-Hartman]

On Wed, Jul 13, 2022 at 02:33:44PM +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@xxxxxxx>
> Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> ---
>  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);

No erroring out?

thanks,

greg k-h