linux-kernel - Re: [PATCH] fs/resctrl: Fix counter auto-assignment on mkdir with mbm

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Message-ID: <437d6c22-f232-48a0-94db-a395aabe85d5@intel.com>
Date: Tue, 16 Sep 2025 14:58:33 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <bp@...en8.de>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs/resctrl: Fix counter auto-assignment on mkdir with
 mbm_event enabled

Hi Babu,

On 9/16/25 10:25 AM, Babu Moger wrote:
> Found that the automatic counter assignment is not working as expected when
> "mbm_event" is enabled. Counters are being assigned regardless of whether
> mbm_assign_on_mkdir is enabled or not.
> 
> The logic was mistakenly placed in rdtgroup_unassign_cntrs() instead of
> rdtgroup_assign_cntrs().
> 
> Fix it by moving the code snippet to rdtgroup_assign_cntrs().
> 

With the goal to address Boris's concerns about changelogs I think the changelog
can be made more specific by replacing the vague "the logic" and "the code snippet"
terms. Below is an example changelog that addresses this but I am afraid that it may
now be considered too much text :(. As I am still learning how to get this right I
surely will not hold up the patch because of this, tag is below.

	rdt_resource::resctrl_mon::mbm_assign_on_mkdir determines if a counter will
	automatically be assigned to an RMID, MBM event pair when its associated
	monitor group is created via mkdir.

	Testing shows that counters are always automatically assigned to new monitor
	groups,	whether	mbm_assign_on_mkdir is set or not.

	To support automatic counter assignment the check for mbm_assign_on_mkdir
	should be in rdtgroup_assign_cntrs() that assigns counters during monitor group
	creation. Instead, the check for mbm_assign_on_mkdir is in rdtgroup_unassign_cntrs()
	that is called on monitor group deletion from where counters should always be
	unassigned, whether mbm_assign_on_mkdir is set or not.

	Fix automatic counter assignment by moving the mbm_assign_on_mkdir check from
	rdtgroup_unassign_cntrs() to rdtgroup_assign_cntrs().

> Fixes: ef712fe97ec57 ("fs/resctrl: Auto assign counters on mkdir and clean up on group removal")
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---

Thank you very much for catching and fixing this issue.

It is not clear to me if the changelog will be acceptable and I provided alternative
text just in case. The fix looks good to me, for that:

Acked-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette