Re: [PATCH v10 2/5] powerpc/crash: introduce a new config option CRASH_HOTPLUG

[Laurent Dufour <ldufour@linux.ibm.com>]

On 23/04/2023 12:52:10, Sourabh Jain wrote:
> Due to CPU/Memory hot plug/unplug or online/offline events the system
> resources changes. A similar change should reflect in the loaded kdump
> kernel kexec segments that describes the state of the CPU and memory of
> the running kernel.
> 
> If the kdump kernel kexec segments are not updated after the CPU/Memory
> hot plug/unplug or online/offline events and kdump kernel tries to
> collect the dump with the stale system resource data then this might
> lead to dump collection failure or an inaccurate dump collection.
> 
> The current method to keep the kdump kernel kexec segments up to date is
> by reloading the complete kdump kernel whenever a CPU/Memory hot
> plug/unplug or online/offline event is observed in userspace. Reloading
> the kdump kernel for every CPU/Memory hot plug/unplug or online/offline
> event is inefficient and creates a large window where the kdump service
> is not available. It can be improved by doing in-kernel updates to only
> necessary kdump kernel kexec segments which describe CPU and Memory
> resources of the running kernel to the kdump kernel.
> 
> The kernel changes related to in-kernel updates to the kdump kernel
> kexec segments are kept under the CRASH_HOTPLUG config option.
> 
> Later in the series, a powerpc crash hotplug handler is introduced to
> update the kdump kernel kexec segments on CPU/Memory hotplug events.
> This arch-specific handler is triggered from a generic crash handler
> that registers with the CPU/Memory add/remove notifiers.
> 
> The CRASH_HOTPLUG config option is enabled by default.
> 
> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> Reviewed-by: Laurent Dufour <laurent.dufour@fr.ibm.com>

I can't remember having sent a review-by on that patch earlier.

Anyway, I can't find any issue with that one, so replace with:
Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>

> ---
>  arch/powerpc/Kconfig | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index a6c4407d3ec83..ac0dc0ffe89b4 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -681,6 +681,18 @@ config CRASH_DUMP
>  	  The same kernel binary can be used as production kernel and dump
>  	  capture kernel.
>  
> +config CRASH_HOTPLUG
> +	bool "In-kernel update to kdump kernel on system configuration changes"
> +	default y
> +	depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG)
> +	help
> +	  Quick and efficient mechanism to update the kdump kernel in the
> +	  event of CPU/Memory hot plug/unplug or online/offline events. This
> +	  approach does the in-kernel update to only necessary kexec segment
> +	  instead of unload-reload entire kdump kernel from userspace.
> +
> +	  If unsure, say Y.
> +
>  config FA_DUMP
>  	bool "Firmware-assisted dump"
>  	depends on PPC64 && (PPC_RTAS || PPC_POWERNV)