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

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Message-ID: <SJ1PR11MB60838CB8BB51EA5B7B9261D6FC67A@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Wed, 28 May 2025 00:14:17 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...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.

> > 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).

-Tony