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

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Date:   Thu, 5 Oct 2023 11:04:27 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....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 James,

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.

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.

Reinette