On 11/7/23 20:29, Russell King (Oracle) wrote:
From: James Morse <james.morse@xxxxxxx> Three of the five ACPI architectures create sysfs entries using register_cpu() for present CPUs, whereas arm64, riscv and all GENERIC_CPU_DEVICES do this for possible CPUs. Registering a CPU is what causes them to show up in sysfs. It makes very little sense to register all possible CPUs. Registering a CPU is what triggers the udev notifications allowing user-space to react to newly added CPUs. To allow all five ACPI architectures to use GENERIC_CPU_DEVICES, change it to use for_each_present_cpu(). Making the ACPI architectures use GENERIC_CPU_DEVICES is a pre-requisite step to centralise their cpu_register() logic, before moving it into the ACPI processor driver. When ACPI is disabled this work would be done by cpu_dev_register_generic(). Of the ACPI architectures that register possible CPUs, arm64 and riscv do not support making possible CPUs present as they use the weak 'always fails' version of arch_register_cpu(). Only two of the eight architectures that use GENERIC_CPU_DEVICES have a distinction between present and possible CPUs. The following architectures use GENERIC_CPU_DEVICES but are not SMP, so possible == present: * m68k * microblaze * nios2 The following architectures use GENERIC_CPU_DEVICES and consider possible == present: * csky: setup_smp() * processor_probe() sets possible for all CPUs and present for all CPUs except the boot cpu, which will have been done by init/main.c::start_kernel(). um appears to be a subarchitecture of x86. The remaining architecture using GENERIC_CPU_DEVICES are: * openrisc and hexagon: where smp_init_cpus() makes all CPUs < NR_CPUS possible, whereas smp_prepare_cpus() only makes CPUs < setup_max_cpus present. After this change, openrisc and hexagon systems that use the max_cpus command line argument would not see the other CPUs present in sysfs. This should not be a problem as these CPUs can't bre brought online as _cpu_up() checks cpu_present(). After this change, only CPUs which are present appear in sysfs. Signed-off-by: James Morse <james.morse@xxxxxxx> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx> --- drivers/base/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
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