linux-kernel - Re: [PATCH 03/18] x86/resctrl: Create helper for RMID allocation and mondata dir creation

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Message-ID: <ec5516e2-521b-084a-ce86-5c371eda2b75@arm.com>
Date:   Tue, 10 Jan 2023 17:57:39 +0000
From:   James Morse <james.morse@....com>
To:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "Chatre, Reinette" <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" 
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        "carl@...amperecomputing.com" <carl@...amperecomputing.com>,
        "lcherian@...vell.com" <lcherian@...vell.com>,
        "bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
        "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>,
        "xingxin.hx@...nanolis.org" <xingxin.hx@...nanolis.org>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        "peternewman@...gle.com" <peternewman@...gle.com>
Subject: Re: [PATCH 03/18] x86/resctrl: Create helper for RMID allocation and
 mondata dir creation

Hi Fenghua,

On 06/01/2023 03:23, Yu, Fenghua wrote:
>> James Morse <james.morse@....com> writes:
>>
>> RMID are allocated for each monitor or control group directory, because each
>> of these needs its own RMID. For control groups,
>> rdtgroup_mkdir_ctrl_mon() later goes on to allocate the CLOSID.
>>
>> MPAM's equivalent of RMID are not an independent number, so can't be
>> allocated until the CLOSID is known. An RMID allocation for one CLOSID may fail,
>> whereas another may succeed depending on how many monitor groups a
>> control group has.
>>
>> The RMID allocation needs to move to be after the CLOSID has been allocated.
>>
>> To make a subsequent change that does this easier to read, move the RMID
>> allocation and mondata dir creation to a helper.

>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 9ce4746778f4..841294ad6263 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -2868,6 +2868,30 @@ static int rdtgroup_init_alloc(struct rdtgroup *rdtgrp)
>>  	return 0;
>>  }
>>
>> +static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp) {
>> +	int ret;
>> +
>> +	if (!rdt_mon_capable)
>> +		return 0;
>> +
>> +	ret = alloc_rmid();
>> +	if (ret < 0) {
>> +		rdt_last_cmd_puts("Out of RMIDs\n");
>> +		return ret;
>> +	}
>> +	rdtgrp->mon.rmid = ret;
>> +
>> +	ret = mkdir_mondata_all(rdtgrp->kn, rdtgrp, &rdtgrp-
>>> mon.mon_data_kn);
>> +	if (ret) {
>> +		rdt_last_cmd_puts("kernfs subdir error\n");


>> +		free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);

                ^^^^^^^^^

>> +		return ret;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>>  			     const char *name, umode_t mode,
>>  			     enum rdt_group_type rtype, struct rdtgroup **r)
>> @@ -2933,20 +2957,10 @@ static int mkdir_rdt_prepare(struct kernfs_node
>> *parent_kn,
>>  		goto out_destroy;
>>  	}
>>
>> -	if (rdt_mon_capable) {
>> -		ret = alloc_rmid();
>> -		if (ret < 0) {
>> -			rdt_last_cmd_puts("Out of RMIDs\n");
>> -			goto out_destroy;
>> -		}
>> -		rdtgrp->mon.rmid = ret;
>> +	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
>> +	if (ret)
>> +		goto out_destroy;
>>
>> -		ret = mkdir_mondata_all(kn, rdtgrp, &rdtgrp-
>>> mon.mon_data_kn);
>> -		if (ret) {
>> -			rdt_last_cmd_puts("kernfs subdir error\n");
>> -			goto out_idfree;
>> -		}
>> -	}
>>  	kernfs_activate(kn);
>>
>>  	/*
>> @@ -2954,8 +2968,6 @@ static int mkdir_rdt_prepare(struct kernfs_node
>> *parent_kn,
>>  	 */
>>  	return 0;
>>
>> -out_idfree:
>> -	free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
>>  out_destroy:
>>  	kernfs_put(rdtgrp->kn);
>>  	kernfs_remove(rdtgrp->kn);

> Why not free allocated rmid? Rmid leak without freed.

It's just moved into the helper.

This free_rmid() is here because this function used to allocate the rmid and the mondata
as separate steps. Now a helper does that in one go - and cleans up after itself.

If mkdir_rdt_prepare_rmid_alloc() fails, it didn't allocate an rmid .. if it secretly did,
it free()s it itself, see the ^-lighted code above.


Thanks,

James