Gautham R Shenoy wrote:
> This patch implements process_freezer based cpu-hotplug
> core.
> The sailent features are:
> o No more (un)lock_cpu_hotplug.
> o No more CPU_LOCK_ACQUIRE and CPU_LOCK_RELEASE. Hence no per-subsystem
> hotcpu mutexes.
> o Calls freeze_process/thaw_processes at the beginning/end of
> the hotplug operation.
...
> @@ -133,7 +111,11 @@ static int _cpu_down(unsigned int cpu)
> if (!cpu_online(cpu))
> return -EINVAL;
>
> - raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
> + if (freeze_processes(FE_HOTPLUG_CPU)) {
> + thaw_processes(FE_HOTPLUG_CPU);
> + return -EBUSY;
> + }
> +
If I'm understanding correctly, this will cause
# echo 0 > /sys/devices/system/cpu/cpuX/online
to sometimes fail, and userspace is expected to try again? This will
break existing applications.
Perhaps drivers/base/cpu.c:store_online should retry as long as
cpu_up/down return -EBUSY. That would avoid a userspace-visible
interface change.
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