Re: [PATCH v6 20/29] init/main: Delay initialization of the lockup detector after smp_init()

[Nicholas Piggin]

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@xxxxxxxxx>

> 
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> ---
> 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
> 
>