linux-kernel - Re: [PATCH v15 02/12] cpu/hotplug: Move idle_thread

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Date:   Tue, 21 Mar 2023 19:20:35 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>,
        Usama Arif <usama.arif@...edance.com>,
        "mark.rutland" <mark.rutland@....com>
Cc:     tglx@...utronix.de, kim.phillips@....com, brgerst@...il.com,
        piotrgorski@...hyos.org, oleksandr@...alenko.name,
        arjan@...ux.intel.com, mingo@...hat.com,
        dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org,
        pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
        fam.zheng@...edance.com, punit.agrawal@...edance.com,
        simon.evans@...edance.com, liangma@...ngbit.com,
        gpiccoli@...lia.com
Subject: Re: [PATCH v15 02/12] cpu/hotplug: Move idle_thread_get() to
 <linux/smpboot.h>

On Mon, 2023-03-20 at 08:17 +0000, David Woodhouse wrote:
> 
> In _cpu_up() the call to idle_thread_get() only happens if the CPU in
> question is starting from CPUHP_OFFLINE but I think that's sufficient?
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 6c0a92ca6bb5..43e0a77f21e8 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -591,12 +591,6 @@ static int bringup_cpu(unsigned int cpu)
>  	struct task_struct *idle = idle_thread_get(cpu);
>  	int ret;
>  
> -	/*
> -	 * Reset stale stack state from the last time this CPU was online.
> -	 */
> -	scs_task_reset(idle);
> -	kasan_unpoison_task_stack(idle);
> -
>  	/*
>  	 * Some architectures have to walk the irq descriptors to
>  	 * setup the vector space for the cpu which comes online.
> @@ -1383,6 +1377,12 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
>  			ret = PTR_ERR(idle);
>  			goto out;
>  		}
> +
> +		/*
> +		 * Reset stale stack state from the last time this CPU was online.
> +		 */
> +		scs_task_reset(idle);
> +		kasan_unpoison_task_stack(idle);
>  	}
>  
>  	cpuhp_tasks_frozen = tasks_frozen;

I put that into a separate commit, rebased on tip/x86/apic and pushed
it out with the rest of the changes to
https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/parallel-6.2-rc3-v16

I'll let Usama do another round of testing and repost it (please).

Thanks!

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