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

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Date:   Thu, 17 Jan 2019 18:35:39 -0800
From:   Atish Patra <atish.patra@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Patrick Stählin <me@...ki.ch>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jason Cooper <jason@...edaemon.net>,
        Alan Kao <alankao@...estech.com>,
        Dmitriy Cherkasov <dmitriy@...-tech.org>,
        Anup Patel <anup@...infault.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Clark <michaeljclark@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Andreas Schwab <schwab@...e.de>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Zong Li <zongbox@...il.com>
Subject: Re: [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up

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.
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
> 

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