Re: [PATCH v3 09/12] fs/resctrl: Reset kernel-mode binding when its rdtgroup goes away

[Babu Moger <babu.moger@amd.com>]

Hi Reinette,

On 6/16/26 18:42, Reinette Chatre wrote:
> Hi Babu,
> 
> On 4/30/26 4:24 PM, Babu Moger wrote:
>> resctrl_kcfg.k_rdtgrp records which rdtgroup currently owns the kernel
>> CLOSID/RMID, but nothing cleared that snapshot when the group was
>> removed.  rmdir of a control or monitor group, or unmount of the
>> resctrl filesystem, left kernel mode enabled on the CPUs the group
>> covered and left k_rdtgrp pointing at freed memory; the next read or write of
>> info/kernel_mode would dereference a stale rdtgroup under rdtgroup_mutex.
> 
> Please do not word the enabling as bugfixes.

Sure.

> 
>>
>> Add rdtgroup_config_kmode_delete() as the disable counterpart of
>> rdtgroup_config_kmode().  It clears the kernel-mode binding on the
>> group's kmode_cpu_mask (or all online CPUs when that mask is empty),
>> drops the per-group kmode/kmode_cpu_mask bookkeeping, and if
>> @rdtgrp was the bound, resets resctrl_kcfg to &rdtgroup_default,
>> BIT(INHERIT_CTRL_AND_MON)) so subsequent sysfs operations resolve
>> to a live group.
> 
> Could you please reword these code descriptions to describe why this
> patch is needed?
> 

Sure.

>>
>> Call it from rdtgroup_rmdir_mon(), rdtgroup_rmdir_ctrl(), and
>> resctrl_fs_teardown(); each call site is gated on rdtgrp->kmode so
>> groups that never participated in kernel mode pay nothing.
> 
> Does this handle the non-default resource groups removed on unmount?
> (see rmdir_all_sub() called from resctrl_fs_teardown())
> 
> (please refer to earlier comments that apply to this patch also)

Yea. I missed free_all_child_rdtgrp() and rmdir_all_sub().  Will fix that.

Thanks
Babu