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Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH net-next v2] ipv4: igmp: annotate data-races around im->users Message-ID: <20260524135938.GA86099@shredder> References: <20260522093906.39764-1-sigefriedhyy@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260522093906.39764-1-sigefriedhyy@gmail.com> X-ClientProxiedBy: FR4P281CA0386.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:f7::14) To SA3PR12MB7901.namprd12.prod.outlook.com (2603:10b6:806:306::12) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA3PR12MB7901:EE_|SN7PR12MB7910:EE_ X-MS-Office365-Filtering-Correlation-Id: ce7ed74e-b741-4edf-8c0a-08deb99cb7a6 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024|22082099003|56012099003|18002099003|11063799006; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?pGQk/5y241Orc52qhm48bk40CgWrg554OeyRDwaeyoIqvMa+wEl1h14+MdR5?= =?us-ascii?Q?FlnqYZHib1X8fXfsHCmWsAEfHGJEPze7kKgn1oRpD8W4Vt2awyzKkMgPa3v2?= =?us-ascii?Q?XVNjs9igkNrQM76I9zaLMjeBni/9SJjvJn5+nsZ4L4lzb/hx1ysUCnj5mMQO?= =?us-ascii?Q?9m06zlKse3jOdzgqOKC/tm5M75EK49kOOiIepXHWYEtNe7Gf0nmJ93HZUhWM?= =?us-ascii?Q?sWtVWdBSv7gbl2QhQsoeYyJDbgSpg4jGvYPINfmI2ApNbE/hhiOgvBb27j0X?= =?us-ascii?Q?cq3/lOnqk7jgvQPipANtz1cWeoWJGA5mFZtsOmalr6jWftiRSh7BFBFT0uyx?= =?us-ascii?Q?Vbi3TKi7+upcgkJZn42z5/u+6sLsmsDeQbC4wn3Ibp0Q9iWsVmWLnbHbDSoc?= =?us-ascii?Q?J5Vfzf6dHbe1ZHMANrgJ8mpEfi3GHaytv2KYRKQOKBFJhaf78POzgtX6HnPB?= =?us-ascii?Q?gRAbDQ1yYPThQDz6JRLOCFp5oEsgaaM4X5hf400SawNffhrBc/ue9PpeF9Bj?= =?us-ascii?Q?jiJUy7tZjqadYy5WtR6d9lsuMbGAJbsaFldqVFkimBs4ThsZCUXWhazYOSHy?= =?us-ascii?Q?eiapFmy0J/MyQMHTzf+dtu7thL5FN2bdodRN/W9q8JvONHN5mNgUeYOMUMZH?= =?us-ascii?Q?HQc58aDR8fI7/PfuUDt99LCA9ekqff0u/2sow2/WLx4rOrdiz6af/3/FzeUo?= =?us-ascii?Q?NHdxH5/s3EH2C6ZGwCggfXmCa+JHfT4UN9X4BqoWKc8xvz0nxq7zBqb1v5I4?= =?us-ascii?Q?kIE7d29+PGP60eS1jnCxSV2wJindFRqkgEQyQoy7VAULw9lH+rNJsLvUBHFT?= =?us-ascii?Q?qzq9v3qTIh4tw2wjxHKNCHJSFWthPid1FrcHz5+eKwV3dejVOKOOcIlmAAAF?= =?us-ascii?Q?ybBnEfemLYuYTu4p2jbqJBpxlsK3fRc5WaQ+o3neyatO8ytqDbhNaoWYY2wZ?= =?us-ascii?Q?98dchy4X92HWQN8JcXqOLnggOggGlxpDax+6ZN+YQ2u3uSQUH0s+qGbOgaxx?= =?us-ascii?Q?Aod7Cm1LoWsB+EdklwcLENyCR2m1IVh/Y0/Ag6FLcTR58qh0Sg5eYgq8rxcH?= =?us-ascii?Q?OnvJs/xRlvqft1YPXVFxUILrZkyPmhniEK69lj8Uj/BpmNPESlqqbvlR9Rdw?= =?us-ascii?Q?JWfV811I2jjotxZyQGeUp01XgSG8qt5UU0T8o89PP4iqpQI6nUJQO/aNWwoR?= =?us-ascii?Q?UrtDmQEg2wY2LJ853DmMeJ5kwu1ntOeYJlbjXfVQo50zEBxeZcbvGoAgdLij?= =?us-ascii?Q?yErC6lCrierkjVX0kbkjstTjIRZfCVEHjqAqVGpwEVuWz3nPNol3ndyHZEzu?= =?us-ascii?Q?vsuSvAsR06p1a8Oictp0ZQtnu/InVEmqPXerXFxON0wVvq8IpdsBW4sjoEih?= =?us-ascii?Q?8xUDRfHtSpj8YwNT0A4utVrleK0nRYITzn+cZfluGotKF/LJQsVewS8V7Kju?= =?us-ascii?Q?AJIUQy3yg7/pf0BzvFvJOhEiLecpnltewPvPzS/0plL/cvIqXrQOrzlKaLMo?= =?us-ascii?Q?K+/pByDqiOF26FzljDTp1iYOje5efq862SRgJT3UlS+tTK/N0kVJFRmrYjMl?= =?us-ascii?Q?6jIOyrpcv/8wUIgtgxN/fAR0/Sv/IQiLw5frdTmSBPkqhAts1CG8RDCY28b6?= =?us-ascii?Q?EkvYAY7YaWc+HZy/SH4k9MxQ694W8s2Npfap7DI4fpyMFlvVJ/46ar1UTgxP?= =?us-ascii?Q?8sJQQ2gSZel1lxZsTUvcNow8bcFDESOMUU+bxAIkf0exqm5N?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: ce7ed74e-b741-4edf-8c0a-08deb99cb7a6 X-MS-Exchange-CrossTenant-AuthSource: SA3PR12MB7901.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 May 2026 13:59:48.1574 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: EIhrPhQMhQw1VWowpKt7uZzuYpdYGTECaCgLSpzaQVu0EGiQYeKZVwDu+cDA237f/NGOtT/ESkcuggLOja13tA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB7910 On Fri, May 22, 2026 at 06:39:06PM +0900, Yuyang Huang wrote: > /proc/net/igmp walks IPv4 multicast memberships under RCU and > prints im->users without holding RTNL, while multicast join and leave > paths update the field while holding RTNL. Annotate this intentional > lockless snapshot with READ_ONCE() and the matching writers with > WRITE_ONCE(). > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Signed-off-by: Yuyang Huang Reviewed-by: Ido Schimmel > --- > Changes in v2: > - Added Fixes: tag > > net/ipv4/igmp.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c > index 27d120183779..f2aca659b29c 100644 > --- a/net/ipv4/igmp.c > +++ b/net/ipv4/igmp.c > @@ -1541,7 +1541,7 @@ static void ____ip_mc_inc_group(struct in_device *in_dev, __be32 addr, > } > > if (im) { > - im->users++; > + WRITE_ONCE(im->users, im->users + 1); > ip_mc_add_src(in_dev, &addr, mode, 0, NULL, 0); > goto out; > } > @@ -1550,7 +1550,7 @@ static void ____ip_mc_inc_group(struct in_device *in_dev, __be32 addr, > if (!im) > goto out; > > - im->users = 1; > + WRITE_ONCE(im->users, 1); This one isn't necessary since the object was just allocated and not yet published