linux-kernel - Re: [PATCH v6 20/29] init/main: Delay initialization of the lockup detector after smp

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Date:   Tue, 10 May 2022 20:38:22 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v6 20/29] init/main: Delay initialization of the lockup
 detector after smp_init()

Excerpts from Ricardo Neri's message of May 6, 2022 9:59 am:
> Certain implementations of the hardlockup detector require support for
> Inter-Processor Interrupt shorthands. On x86, support for these can only
> be determined after all the possible CPUs have booted once (in
> smp_init()). Other architectures may not need such check.
> 
> lockup_detector_init() only performs the initializations of data
> structures of the lockup detector. Hence, there are no dependencies on
> smp_init().

I think this is the only real thing which affects other watchdog types?

Not sure if it's a big problem, the secondary CPUs coming up won't
have their watchdog active until quite late, and the primary could
implement its own timeout in __cpu_up for secondary coming up, and
IPI it to get traces if necessary which is probably more robust.

Acked-by: Nicholas Piggin <npiggin@...il.com>

> 
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
> Cc: iommu@...ts.linux-foundation.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: x86@...nel.org
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
> Changes since v5:
>  * Introduced this patch
> 
> Changes since v4:
>  * N/A
> 
> Changes since v3:
>  * N/A
> 
> Changes since v2:
>  * N/A
> 
> Changes since v1:
>  * N/A
> ---
>  init/main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/init/main.c b/init/main.c
> index 98182c3c2c4b..62c52c9e4c2b 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1600,9 +1600,11 @@ static noinline void __init kernel_init_freeable(void)
>  
>  	rcu_init_tasks_generic();
>  	do_pre_smp_initcalls();
> -	lockup_detector_init();
>  
>  	smp_init();
> +
> +	lockup_detector_init();
> +
>  	sched_init_smp();
>  
>  	padata_init();
> -- 
> 2.17.1
> 
>