linux-kernel - Re: [PATCH] x86/resctrl: Remove unnecessary references to cacheinfo in the resctrl subsystem.

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Message-ID: <45091ad1-e366-4c56-be94-e15c693da520@intel.com>
Date: Tue, 27 May 2025 19:59:51 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, Qinyun Tan
	<qinyuntan@...ux.alibaba.com>
CC: "H . Peter Anvin" <hpa@...or.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86/resctrl: Remove unnecessary references to cacheinfo
 in the resctrl subsystem.

Hi Tony,

On 5/27/25 5:14 PM, Luck, Tony wrote:
>>> 2. Lifecycle dependency: The cacheinfo structure's lifecycle is managed
>>> by the cache subsystem, making it unsafe for resctrl to hold
>>> long-term references.
>>
>> This is not obvious to me. Could you please elaborate how resctrl could
>> have a reference to a removed structure?
> 
> get_cpu_cacheinfo_level() returns a pointer to a per-cpu structure.
> 
> While it appears that those don't get freed and re-used when a CPU is
> taken offline, it does seem highly dubious to keep using one for an
> offline CPU (which is what happens if the first CPU that comes online
> in a domain is taken offline).

I do not understand what your goal is with this response. You seem to
both defend and refute this "lifecycle dependency" motivation/claim. 

I am not disagreeing with this fix but I would like to ensure that I
understand all motivations for it.

Reinette