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SubjectRe: [PATCH 03/18] x86/resctrl: Create helper for RMID allocation and mondata dir creation
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Hi Fenghua,

On 06/01/2023 03:23, Yu, Fenghua wrote:
>> James Morse <james.morse@arm.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
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