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

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Date:   Thu, 5 Oct 2023 18:06:19 +0100
From:   James Morse <james.morse@....com>
To:     babu.moger@....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>,
        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 Babu,

On 04/10/2023 19:00, Moger, Babu wrote:
> On 9/14/23 12:21, 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_exit_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.

>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 85ceaf9a31ac..57cf1e6a57bd 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -537,6 +537,7 @@ void closid_free(int closid);
>>  int alloc_rmid(void);
>>  void free_rmid(u32 rmid);
>>  int rdt_get_mon_l3_config(struct rdt_resource *r);
>> +void resctrl_exit_mon_l3_config(struct rdt_resource *r);
>>  bool __init rdt_cpu_has(int flag);
>>  void mon_event_count(void *info);
>>  int rdtgroup_mondata_show(struct seq_file *m, void *arg);
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index ded1fc7cb7cb..cfb3f632a4b2 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -741,6 +741,16 @@ static int dom_data_init(struct rdt_resource *r)
>>  	return 0;
>>  }
>>  
>> +void resctrl_exit_mon_l3_config(struct rdt_resource *r)
>> +{
>> +	mutex_lock(&rdtgroup_mutex);
>> +
>> +	kfree(rmid_ptrs);
>> +	rmid_ptrs = NULL;
>> +
>> +	mutex_unlock(&rdtgroup_mutex);
>> +}

> What is the need for passing "rdt_resource *r" here?

My vain belief that monitors should be supported on something other than L3, but I agree
that isn't what resctrl does today. I'll remove it.


> Is mutex_lock required?

Reads and writes to rmid_ptrs[] are protected by that lock. This ensures no-one reads the
value while its being free()d, and after this function releases the lock, anyone trying
sees NULL.

(This is all moot as its only caller is marked __exit, so gets discarded by the linker)



Thanks,

James