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

[Reinette Chatre]

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.

> 
> 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?

> 
> 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)

Reinette