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

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Date: Tue, 20 Feb 2024 16:27:45 +0100
From: David Hildenbrand <david@...hat.com>
To: James Morse <james.morse@....com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>,
 Thomas Gleixner <tglx@...utronix.de>, 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 13.02.24 19:44, James Morse wrote:
> rmid_ptrs[] is allocated from dom_data_init() but never free()d.
> 
> While the exit text ends up in the linker script's DISCARD section,
> the direction of travel is for resctrl to be/have loadable modules.
> 
> Add resctrl_put_mon_l3_config() to cleanup any memory allocated
> by rdt_get_mon_l3_config().
> 
> There is no reason to backport this to a stable kernel.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Tested-by: Babu Moger <babu.moger@....com>
> Tested-by: Carl Worth <carl@...amperecomputing.com> # arm64
> Reviewed-by: Babu Moger <babu.moger@....com>
> ---

[...]


> +static void __exit dom_data_exit(void)
> +{
> +	mutex_lock(&rdtgroup_mutex);
> +
> +	kfree(rmid_ptrs);
> +	rmid_ptrs = NULL;
> +
> +	mutex_unlock(&rdtgroup_mutex);

Just curious: is grabbing that mutex really required?

Against which race are we trying to protect ourselves?

I suspect this mutex is not required here: if we could racing with 
someone else, likely freeing that memory would not be safe either.

Apart from that LGTM.

-- 
Cheers,

David / dhildenb