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Subject: Re: [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up
To:     Christoph Hellwig <hch@infradead.org>
Cc:     =?UTF-8?Q?Patrick_St=c3=a4hlin?= <me@packi.ch>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Jason Cooper <jason@lakedaemon.net>,
        Alan Kao <alankao@andestech.com>,
        Dmitriy Cherkasov <dmitriy@oss-tech.org>,
        Anup Patel <anup@brainfault.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michael Clark <michaeljclark@mac.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Andreas Schwab <schwab@suse.de>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Zong Li <zongbox@gmail.com>
References: <1546940318-9752-1-git-send-email-atish.patra@wdc.com>
 <1546940318-9752-2-git-send-email-atish.patra@wdc.com>
 <20190115135125.GA28946@infradead.org>
From:   Atish Patra <atish.patra@wdc.com>
Message-ID: <1995e941-a8cf-c12e-71ae-7b50cf6c0ca5@wdc.com>
Date:   Thu, 17 Jan 2019 18:35:39 -0800
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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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