linux-kernel - Re: [PATCH v6 02/24] x86/resctrl: kfree() rmid_ptrs from rdtgroup

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Date:   Wed, 25 Oct 2023 18:56:58 +0100
From:   James Morse <james.morse@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...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,
        xingxin.hx@...nanolis.org, 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 v6 02/24] x86/resctrl: kfree() rmid_ptrs from
 rdtgroup_exit()

Hi Reinette,

On 05/10/2023 19:04, Reinette Chatre wrote:
> On 10/5/2023 10:05 AM, James Morse wrote:
>> On 02/10/2023 18:00, Reinette Chatre wrote:
>>> On 9/14/2023 10:21 AM, James Morse wrote:
>>>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> index 725344048f85..a2158c266e41 100644
>>>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> @@ -3867,6 +3867,11 @@ int __init rdtgroup_init(void)
>>>>  
>>>>  void __exit rdtgroup_exit(void)
>>>>  {
>>>> +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>>>> +
>>>> +	if (r->mon_capable)
>>>> +		resctrl_exit_mon_l3_config(r);
>>>> +
>>>>  	debugfs_remove_recursive(debugfs_resctrl);
>>>>  	unregister_filesystem(&rdt_fs_type);
>>>>  	sysfs_remove_mount_point(fs_kobj, "resctrl");
>>>
>>> You did not respond to me when I requested that this be done differently [1].
>>> Without a response letting me know the faults of my proposal or following the
>>> recommendation I conclude that my feedback was ignored. 
>>
>> Not so - I just trimmed the bits that didn't need a response. I can respond 'Yes' to each
>> one if you prefer, but I find that adds more noise than signal.
> 
> I do not expect a response to every review feedback but no response
> is assumed to mean that you agree with the feedback.
> 
>>
>> This is my attempt at 'doing the cleanup properly', which is what you said your preference
>> was. (no machine on the planet can ever run this code, the __exit section is always
>> discarded by the linker).
>>
>> Reading through again, I missed that you wanted this called from resctrl_exit(). (The
> 
> Right. And not responding to that created expectation that you agreed with the
> request.
> 
>> naming suggests I did this originally, but it didn't work out).
>> I don't think this works as the code in resctrl_exit() remains part of the arch code after
>> the move, but allocating rmid_ptrs[] stays part of the fs code.
>>
>> resctrl_exit() in core.c gets renamed as resctrl_arch_exit(), and rdtgroup_exit() takes on
>> the name resctrl_exit() as its part of the exposed interface.
> 
> I expect memory allocation/free to be symmetrical. Doing otherwise
> complicates the code. Having this memory freed in rdtgroup_exit() only
> seems appropriate if it is allocated from rdtgroup_init().
> Neither rmid_ptrs[] nor closid_num_dirty_rmid are allocated in
> rdtgroup_init() so freeing it in rdtgroup_exit() is not appropriate.

It probably makes more sense when you see how things get split up. I was trying to reduce
the churn of adding something in one place, then moving it later.

For now I've added all the functions to make this thing symmetric.



James


> If you are planning to move resctrl_exit() to be arch code then I expect
> resctrl_late_init() to be split with the rmid_ptrs[]/closid_num_dirty_rmid
> allocation moving to fs code. Freeing that memory can follow at that time.