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Thu, 8 Oct 2026 22:21:52 +0000 Message-ID: Date: Thu, 8 Oct 2026 15:21:48 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 01/25] fs/resctrl: Ensure default group reports tasks on monitor-only systems To: Tony Luck , Fenghua Yu , "Maciej Wieczor-Retman" , Peter Newman , James Morse , Babu Moger , Drew Fustini , Dave Martin , Chen Yu , David E Box , CC: Christoph Hellwig , , , Sashiko References: <20260928221509.68002-1-tony.luck@intel.com> <20260928221509.68002-2-tony.luck@intel.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <20260928221509.68002-2-tony.luck@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR04CA0154.namprd04.prod.outlook.com (2603:10b6:303:85::9) To IA0PR11MB8379.namprd11.prod.outlook.com (2603:10b6:208:488::20) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR11MB8379:EE_|DS0PR11MB7335:EE_ X-MS-Office365-Filtering-Correlation-Id: 083506c4-f51e-40ed-c041-08df258a8dcb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|23010399003|366016|921020|56012099006|4143699003|6133799003|11063799006|10067099003|5023799004|18002099003|22082099003; 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It looks like my comments regarding tip changelog requirements are still being missed. It is highly time-consuming to manually verify every claim made within these changelogs, and then separately draft feedback on where they fail to meet the documented tip requirements. You inspired me to automate these steps. I created a "changelog checker" that automatically verifies the claims and checks the changelog against the documented tip requirements. These are the standard, straightforward expectations for our submissions. The tool will handle reviews of your changelogs instead of me so I don't lose any more manual review time. You can coordinate directly with the bot's feedback now! Here is what it has to say about this changelog: Verified claims - rdtgroup_tasks_show() → show_rdt_tasks() → is_closid_match() — CONFIRMED (that is the chain in fs/resctrl/rdtgroup.c). - resctrl_arch_alloc_capable() false on monitor-only systems makes is_closid_match() return false for all tasks — CONFIRMED (x86 returns rdt_alloc_capable, set once in resctrl_cpu_detect() and never cleared; rdt_get_tree() permits a mount with monitoring alone). - The default group has type RDTCTRL_GROUP, so is_rmid_match() also returns false — CONFIRMED (rdtgroup_setup_default() sets type = RDTCTRL_GROUP; is_rmid_match() requires RDTMON_GROUP). - The root tasks file appears empty — CONFIRMED. The file always exists on a monitor-only mount; it carries RFTYPE_BASE, which rdt_get_tree() passes unconditionally. - A RDTCTRL_GROUP other than the default can only be created when allocation is supported — CONFIRMED (rdtgroup_mkdir() gates rdtgroup_mkdir_ctrl_mon() on resctrl_arch_alloc_capable()). - "whenever the remaining resctrl_arch_match_closid() check could meaningfully succeed, resctrl_arch_alloc_capable() was already implicitly true, making the test redundant" — FALSE. rdtgroup_setup_default() sets closid = RESCTRL_RESERVED_CLOSID, and every task that has not been moved keeps that CLOSID, so resctrl_arch_match_closid() succeeds for the default group while resctrl_arch_alloc_capable() is false. That is the case the patch fixes. - Fixes: e6b2fac36fcc — CONFIRMED. That commit introduced the capability test into the tasks-file path, and its own changelog asserted "This is harmless as rdtgroup_mkdir() tests these capable flags", which overlooked the default group. Findings [R18][R9] must-fix The safety argument contradicts the bug being fixed The last paragraph concludes the removed test was redundant. If it were redundant the patch would be a no-op. The default group is the one group whose result changes, and the parenthetical that excludes it from the first sentence is not carried into the second. Scope the claim: redundant for every other CTRL_MON group, wrong for the default group. [R5][R6][R24] should-fix No context paragraph; the problem leads The body opens by naming the offending check. A reader has not yet been told that resctrl can be mounted with monitoring only, that the default group owns every unassigned task, or that CTRL_MON membership is decided by CLOSID. Without that, the problem paragraph has nothing to attach to. [R12] should-fix No imperative solution sentence "Removing the resctrl_arch_alloc_capable() test is safe because ..." is a gerund, and the patch never says "Drop ...". The tip tree asks for the fix in the imperative. [R8] should-fix Three paragraphs re-derive a one-term removal The indented call chain, then "is_closid_match() unconditionally returns false for all tasks", then the empty-file effect all restate the same single condition. The user-visible symptom plus the reason both match tests fail is enough. [R20] nit "This is a pre-existing issue, but ..." This addresses the series reviewer, not a future reader of the commit. The Fixes: tag already conveys that the bug predates the series; such notes belong below the --- line. [R13] nit "actively breaks" — "breaks" carries the same meaning. [R23][RC5] nit Prose uses `type == RDTCTRL_GROUP` Documentation/filesystems/resctrl.rst calls these "CTRL_MON" groups and the root-owned ones "MON" groups. Those are the terms of art a reviewer can map to the interface without opening the diff. Tag ordering (Fixes → Reported-by → Closes → Signed-off-by) matches R21. Wrapping is 70–76 columns, within RC4 — checkpatch's single "Prefer a maximum 75 chars" warning is not reportable for resctrl. > > When a user reads the root /sys/fs/resctrl/tasks file on a system with > monitoring capabilities but no allocation capabilities, the following call > chain occurs: > rdtgroup_tasks_show() > show_rdt_tasks() > is_closid_match() > > Since resctrl_arch_alloc_capable() evaluates to false on such systems, > is_closid_match() unconditionally returns false for all tasks. Furthermore, > because the default group has type RDTCTRL_GROUP, is_rmid_match() will also > return false. > > This causes the root tasks file to appear completely empty, hiding all tasks > on the system that have not been explicitly moved to a monitoring group. > > Removing the resctrl_arch_alloc_capable() test is safe because a struct > rdtgroup with type == RDTCTRL_GROUP (other than the always-present default > group) can only be created on systems where allocation is supported. So > whenever the remaining resctrl_arch_match_closid() check could meaningfully > succeed, resctrl_arch_alloc_capable() was already implicitly true, making > the test redundant. > > Fixes: e6b2fac36fcc ("x86/resctrl: Use is_closid_match() in more places") > Reported-by: Sashiko > Closes: https://sashiko.dev/#/patchset/20260831174421.13921-1-tony.luck%40intel.com?part=9 > Signed-off-by: Tony Luck > --- Reinette