linux-kernel - Re: [PATCH v17 13/32] x86,fs/resctrl: Add an architectural hook called for each mount

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Message-ID: <aVwTcX7V_HN2j6SW@agluck-desk3>
Date: Mon, 5 Jan 2026 11:39:29 -0800
From: "Luck, Tony" <tony.luck@...el.com>
To: Borislav Petkov <bp@...en8.de>
CC: Fenghua Yu <fenghuay@...dia.com>, Reinette Chatre
	<reinette.chatre@...el.com>, Maciej Wieczor-Retman
	<maciej.wieczor-retman@...el.com>, Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>, "Drew
 Fustini" <dfustini@...libre.com>, Dave Martin <Dave.Martin@....com>, Chen Yu
	<yu.c.chen@...el.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v17 13/32] x86,fs/resctrl: Add an architectural hook
 called for each mount

On Mon, Jan 05, 2026 at 08:17:11PM +0100, Borislav Petkov wrote:
> On Wed, Dec 17, 2025 at 09:21:00AM -0800, Tony Luck wrote:
> > +void resctrl_arch_pre_mount(void)
> > +{
> > +	static atomic_t only_once = ATOMIC_INIT(0);
> > +	int old = 0;
> > +
> > +	if (!atomic_try_cmpxchg(&only_once, &old, 1))
> > +		return;
> > +}
> 
> There's
> 
> #define DO_ONCE(func, ...)
> 
> Can't use that?

Learn something new every day. Yes, <linux/once.h> looks possible here.

Though I believe I'll need the DO_ONCE_SLEEPABLE() version since 
resctrl_arch_pre_mount() grabs a mutex and various called functions
allocate memory using kmalloc().

-Tony