Re: [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up

[Atish Patra]

On 1/15/19 5:51 AM, Christoph Hellwig wrote:
> >   
> >   void *__cpu_up_stack_pointer[NR_CPUS];
> >   void *__cpu_up_task_pointer[NR_CPUS];
> > +static DECLARE_COMPLETION(cpu_running);
> >   
> >   void __init smp_prepare_boot_cpu(void)
> >   {
> > @@ -81,6 +82,7 @@ void __init setup_smp(void)
> >   
> >   int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> >   {
> > +	int ret = 0;
> >   	int hartid = cpuid_to_hartid_map(cpu);
> >   	tidle->thread_info.cpu = cpu;
> >   
> > @@ -96,10 +98,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> >   		  task_stack_page(tidle) + THREAD_SIZE);
> >   	WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
> >   
> > -	while (!cpu_online(cpu))
> > -		cpu_relax();
> > +	wait_for_completion_timeout(&cpu_running,
> > +					    msecs_to_jiffies(1000));
>
> Having a global completion here worries me.  I bet we have some higher
> level serialization, but can we comment or even better lockdep assert on
> that?

Yes. It is serialized from smp.c in smp_init(). It brings one cpu online
at a time for preset_cpu mask.

Do we still need a lockdep assert ?

Regards,
Atish
> Also please use up your available lines (72 in commit logs, 80 in source
> files) instead of adding spurious line wraps.
>
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