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Tue, 7 Apr 2026 20:50:52 +0000 Message-ID: Date: Tue, 7 Apr 2026 13:50:50 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 03/13] fs/resctrl: Avoid "may be used uninitialized" warning To: Borislav Petkov CC: , , , , , , , , , , , , , References: <56fa3b5937ec6fda4eec162393463d8dbfc1abe4.1775576382.git.reinette.chatre@intel.com> <20260407185543.GFadVTLy82sBzT3eej@fat_crate.local> Content-Language: en-US From: Reinette Chatre In-Reply-To: <20260407185543.GFadVTLy82sBzT3eej@fat_crate.local> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR04CA0158.namprd04.prod.outlook.com (2603:10b6:303:85::13) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) 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: SJ2PR11MB7573:EE_|PH0PR11MB5902:EE_ X-MS-Office365-Filtering-Correlation-Id: 035dd85d-54b7-44b4-c0df-08de94e75b69 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7416014|56012099003|22082099003|18002099003; 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On 4/7/26 11:55 AM, Borislav Petkov wrote: > On Tue, Apr 07, 2026 at 09:02:00AM -0700, Reinette Chatre wrote: >> Building resctrl with extra checks ("W=12") produces the following warning: >> .../include/linux/ucopysize.h:22:17: warning: ‘buf’ may be used uninitialized [-Wmaybe-uninitialized] >> 22 | __check_object_size(ptr, n, to_user); >> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> .../include/linux/ucopysize.h: In function ‘pseudo_lock_measure_trigger’: >> .../include/linux/ucopysize.h:10:13: note: by argument 1 of type ‘const void *’ to ‘__check_object_size’ declared here >> 10 | extern void __check_object_size(const void *ptr, unsigned long n, >> | ^~~~~~~~~~~~~~~~~~~ >> .../fs/resctrl/pseudo_lock.c:754:14: note: ‘buf’ declared here >> 754 | char buf[32]; >> | ^~~ >> >> __check_object_size() ensures the provided buffer is within a valid location >> but does not read from the uninitialized buffer. Even so, initialize the >> buffer to silence the warning to help resctrl have a cleaner build. >> >> Signed-off-by: Reinette Chatre >> --- >> fs/resctrl/pseudo_lock.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/resctrl/pseudo_lock.c b/fs/resctrl/pseudo_lock.c >> index fa3687d69ebd..e1e9134474f4 100644 >> --- a/fs/resctrl/pseudo_lock.c >> +++ b/fs/resctrl/pseudo_lock.c >> @@ -750,8 +750,8 @@ static ssize_t pseudo_lock_measure_trigger(struct file *file, >> size_t count, loff_t *ppos) >> { >> struct rdtgroup *rdtgrp = file->private_data; >> + char buf[32] = {}; > > AFAIU, you're not leaking any uninitialized stack data from that buffer, > right? Right. From what I can tell __check_object_size() just checks that the address is from a valid region and does not read from the buffer. > > If so, why do you care about some silly build warning and are willing to waste > a 32-byte memset on every function entry? I care because I am including a W=12 build as part of checking all resctrl patches and having this be the one and only warning that always shows up is distracting. Removing it to accomplish a clean W=12 build does not seem impactful to me. Of course you are right that this wastes a memset. This function is not on a hot path though and I do not believe it would be called frequently since it is intended to demonstrate how successful the setup of a pseudo-lock region was and successive calls should produce consistent results. > > There's a reason those warnings are behind W= ... Indeed. This patch is for developer and maintenance convenience and not required for resctrl health. No problem from me if you find it not to be appropriate. I will just continue to parse the warning out of the logs. Reinette