linux-kernel - Re: [RFC PATCH v3 04/10] sched/core: Dont allow to use CPU marked as paravirt

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Message-ID: <c9ab1c85-f868-4a4a-ada9-58df502ffe3d@linux.ibm.com>
Date: Thu, 11 Sep 2025 20:14:00 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: vschneid@...hat.com, iii@...ux.ibm.com, huschle@...ux.ibm.com,
        rostedt@...dmis.org, dietmar.eggemann@....com, vineeth@...byteword.org,
        jgross@...e.com, pbonzini@...hat.com, seanjc@...gle.com,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, tglx@...utronix.de, yury.norov@...il.com,
        maddy@...ux.ibm.com, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, gregkh@...uxfoundation.org
Subject: Re: [RFC PATCH v3 04/10] sched/core: Dont allow to use CPU marked as
 paravirt



On 9/11/25 10:46 AM, K Prateek Nayak wrote:
> Hello Shrikanth,
> 

Hi Prateek, Thanks for looking into this.

> On 9/10/2025 11:12 PM, Shrikanth Hegde wrote:
>> @@ -2462,8 +2462,13 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
>>   		return cpu_online(cpu);
>>   
>>   	/* Non kernel threads are not allowed during either online or offline. */
>> -	if (!(p->flags & PF_KTHREAD))
>> -		return cpu_active(cpu);
>> +	if (!(p->flags & PF_KTHREAD)) {
>> +		/* A user thread shouldn't be allowed on a paravirt cpu */
>> +		if (is_cpu_paravirt(cpu))
>> +			return false;
>> +		else
> 
> nit. redundant "else". I think this can be simplified as:
>

alright.
>      return !is_cpu_paravirt(cpu) && cpu_active(cpu);
> 
>> +			return cpu_active(cpu);
>> +	}
>