linux-kernel - Re: [PATCH v9 02/24] x86/resctrl: kfree() rmid_ptrs from resctrl

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Date: Tue, 20 Feb 2024 17:12:55 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: James Morse <james.morse@....com>, David Hildenbrand <david@...hat.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre
 <reinette.chatre@...el.com>, Ingo Molnar <mingo@...hat.com>, Borislav
 Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>, Babu Moger
 <Babu.Moger@....com>, shameerali.kolothum.thodi@...wei.com, D Scott
 Phillips OS <scott@...amperecomputing.com>, carl@...amperecomputing.com,
 lcherian@...vell.com, bobo.shaobowang@...wei.com,
 tan.shaopeng@...itsu.com, baolin.wang@...ux.alibaba.com, Jamie Iles
 <quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
 peternewman@...gle.com, dfustini@...libre.com, amitsinght@...vell.com
Subject: Re: [PATCH v9 02/24] x86/resctrl: kfree() rmid_ptrs from
 resctrl_exit()

On Tue, Feb 20 2024 at 16:01, James Morse wrote:
> On 20/02/2024 15:54, Thomas Gleixner wrote:
>>> With MPAM this code can be invoked from an error IRQ signalled by the hardware, so it
>>> could happen anytime.
>> 
>> Which does not work because you can't acquire a mutex from hard
>> interrupt context.
>
> Indeed - which is why that happens via schedule_work() [0]
>
> My point was that its non-obvious where/when this will happen, so taking the lock and
> forgetting about it is the simplest thing to do.

Makes sense.

Thanks,

        tglx