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

Atish Patra
2019-01-18T02:35:42Z

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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