Re: [patch 01/18] init: Pin init task to boot cpu initially

Steven Rostedt
2017-05-15T14:10:35Z

On Sun, 14 May 2017 20:27:17 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:

> Some of the boot code in init_kernel_freeable() which runs before SMP
> bringup assumes (rightfully) that it runs on the boot cpu and therefor can
> use smp_processor_id() in preemptible context.
>
> That works so far because the smp_processor_id() check starts to be
> effective after smp bringup. That's just wrong. Starting with SMP bringup
> and the ability to move threads around, smp_processor_id() in preemptible
> context is broken.
>
> Aside of that it does not make sense to allow init to run on all cpus
> before sched_smp_init() has been run.
>
> Pin the init to the boot cpu so the existing code can continue to use
> smp_processor_id() without triggering the checks when the enabling of those
> checks starts earlier.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> ---
> init/main.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1015,10 +1015,13 @@ static noinline void __init kernel_init_
> * init can allocate pages on any node
> */
> set_mems_allowed(node_states[N_MEMORY]);
> +
> /*
> - * init can run on any cpu.
> + * Pin init on the boot cpu. Task migration is not properly working
> + * until sched_init_smp() has been run. It will set the allowed
> + * cpus for init to the non isolated cpus.
> */
> - set_cpus_allowed_ptr(current, cpu_all_mask);
> + set_cpus_allowed_ptr(current, cpumask_of(raw_smp_processor_id()));
>
> cad_pid = task_pid(current);
>
>