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Miller" , Jakub Kicinski , Paolo Abeni , David Ahern , Simon Horman , netdev@vger.kernel.org, eric.dumazet@gmail.com, Taehee Yoo Subject: Re: [PATCH v2 net 4/5] ipv6: mcast: use rcu_assign_pointer() for __rcu list updates Message-ID: <20260830154514.GD2974032@shredder> References: <20260828084531.1826790-1-edumazet@google.com> <20260828084531.1826790-5-edumazet@google.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260828084531.1826790-5-edumazet@google.com> X-ClientProxiedBy: FR4P281CA0206.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:e5::10) To PH0PR12MB7957.namprd12.prod.outlook.com (2603:10b6:510:281::22) 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: PH0PR12MB7957:EE_|IA1PR12MB8223:EE_ X-MS-Office365-Filtering-Correlation-Id: e6377e52-d298-49ef-f37b-08df06adb476 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|23010399003|366016|56012099006|10067099003|11063799006|4143699003|18002099003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?a9lAvuPI5H2mZjgL0W2lao4C4mhukp1dNFM8jobO4F85aQHk9QK53M/iY9k/?= =?us-ascii?Q?/baPAtfMGewMoB5Sv0rAmWGETH0DePM/V2RIxaKpvGwIcziniWChF06nFals?= =?us-ascii?Q?+5hyNs4Xq61EIGrSIRYjqWoUr15hPyolDiFXRGCorpHcYbCiRvtF/qp1mIZY?= =?us-ascii?Q?gF9QcLO6DThVVtdmLDYysd7oRinxARkxd7cvTCvv8Zpia3Gn+Qx5QnNHoou4?= =?us-ascii?Q?ReREXSOA4eBeLukBR8JoplKQWml4pdz0Z5wgCoQzFPiGyJYStpkqeG0UQcNf?= =?us-ascii?Q?zSv04GcP+BBlk5ktQ75tOmpgJW5zKMhLA7QR4bNUbMinucQsEjzEceh1zj8e?= =?us-ascii?Q?1zc4DPEp+mNzHKZtg2ROFtA3tjItcV5AbVsQpk5WE1MI6+e/bsynyllnmEdQ?= =?us-ascii?Q?G2nnKQrLJ2hE+Lf4J42mU6e/POg4djG8Gk/TG6mPZHQAIQ7xTOl74trr6/FT?= =?us-ascii?Q?iCrnmLyQc/IKyR7+BUk3tXyfqItDuCuJD4yrDSp34zI2eMcn62WowZunTdqV?= =?us-ascii?Q?WkaU7W6GPUFY28Ky2dG9JRsiX5ZFZDQ3MgAYeMgUzHftHBKJHdajIh5Gj2/9?= =?us-ascii?Q?czcOmQFqy7hnaYlwB+LyVdqjT78Yhep8LOeyFZyZnSZFDuuKinDr/V9HOJWR?= =?us-ascii?Q?6zmSexCP5T8GWoVJuZvUxW3H7mj5squJgxarU23oJic2d31wK4qDvw3oNFR7?= =?us-ascii?Q?nKab/TAEKns2lQACIjYRciXgPAWhVCIjiLcwNOnAJB2C/a2Tig6PejAC6AOc?= =?us-ascii?Q?FPvhDkyskgmSohxk7BXY6uNK2TwNXSNHlNCHz7udfthYIYUDzlSQHrB4SDHd?= =?us-ascii?Q?B+V6Qjpwr1nDdT002Rn+1FSZzJt8qb4UXRiYtyN27fRsMUCWUE8ZWfgh0K56?= =?us-ascii?Q?aDxv69T7XhRLfF8mtdDr4ndAdCc6n+AL7A15ZfZ+6sX3r9rLi/U1qKyV8dbv?= =?us-ascii?Q?cyWREvGigb+RfaDzvLIvRQ2VMkIgtl0aCwEFXmeAKZysTZhHFwbK8PYy8MsI?= =?us-ascii?Q?E+yDP55hS/wMbGbHKHfrEKz9S+YT8AHJyAqtExDZLK740JhXvjLAw4LV2igc?= =?us-ascii?Q?PajqBLkQW5VwXBBWWfA4ptVosvdUTTnWptpzYWAlZhsQS9hyZcfSZotcaq3+?= =?us-ascii?Q?Xu42Okzw7Jo1O0/OcL4ry0YGPKk2drneBNEM7Wd3J6+MWNEuElbI7vOdRGbX?= =?us-ascii?Q?lleMoGNYNYF1dB9TK6j1WFsetYvt1JS3q5m+5bzviZZN01mSBLTw/XiSzDud?= =?us-ascii?Q?GxG0yFABdVDXdGS61r5b2vvIwH521Y2P7eXwVhAUTOf7Ox8RFX7RsGwnGgul?= =?us-ascii?Q?sl1kRV1ReDunTrgvdepYWBjfHnybjJlxXJDZZQU6feNCf/fkmgGVTxSwCwrk?= =?us-ascii?Q?RtLFVSL4UjtHkCFtCzXdXDtnA+OZuJH614f1mg6fstFKAG0+5vQm14rkdsKT?= =?us-ascii?Q?4IEuXtKTt3pvXG0Jhtdj+tj2hXWg5V+8Oejfgzxs5wXa/66CUukesQQ0RnxP?= =?us-ascii?Q?MBSOw3D52EpSGzjxg315ARZNWOVYcsQ4M6lP2x2LhAF91y0yacZA04yPLLc7?= =?us-ascii?Q?w4XC2NaHeoX1MUUQ5nPWD2z7+g9U3cRu+QUrXBUajBHKN9JTirVQ+icb1Hac?= =?us-ascii?Q?Va8lflsqd2OfmnqEE1HF2KiiCHnNNWMhHHqJn9YnqSaQHxg7mZnlBlNMGrrt?= =?us-ascii?Q?bQ9j9Kv87oqigYNDk6f7mBfPXX+UCZXZyrXgiWhe/Y+G90qH?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: e6377e52-d298-49ef-f37b-08df06adb476 X-MS-Exchange-CrossTenant-AuthSource: PH0PR12MB7957.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Aug 2026 15:45:23.8646 (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: lwobLDSrSBi0I82RRS/e4MCctg/XH/tz7yg3xj2OxnUQOD/VOBTaJfgL39Kwk53Rm6qpXE+Jx7oH2QU6tEu6Rw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB8223 On Fri, Aug 28, 2026 at 08:45:30AM +0000, Eric Dumazet wrote: > Several places in net/ipv6/mcast.c update RCU-protected lists > (np->ipv6_mc_list, idev->mc_list, idev->mc_tomb) using direct pointer > assignments instead of rcu_assign_pointer(): > > 1. In __ipv6_dev_mc_dec(), unlinking a group from idev->mc_list did: > *map = ma->next; > without rcu_assign_pointer() while concurrent readers traverse > idev->mc_list locklessly under rcu_read_lock(). > 2. In ipv6_sock_mc_drop() and __ipv6_sock_mc_close(), unlinking a group > from np->ipv6_mc_list directly assigned *lnk = mc_lst->next and > np->ipv6_mc_list = mc_lst->next without rcu_assign_pointer(), racing > with lockless readers in inet6_mc_check(). > 3. In __ipv6_sock_mc_join(), mc_lst->next was initialized to > np->ipv6_mc_list via raw assignment before publishing mc_lst. > 4. In mld_del_delrec() and __ipv6_dev_mc_inc(), __rcu source pointers > passed into rcu_assign_pointer() lacked explicit dereference helpers. > > Fix these by consistently using rcu_assign_pointer() along with > mc_dereference() / sock_dereference(). > > Fixes: 456b61bca8ee ("ipv6: mcast: RCU conversion") > Fixes: 88e2ca308094 ("mld: convert ifmcaddr6 to RCU") > Signed-off-by: Eric Dumazet > Cc: Taehee Yoo Reviewed-by: Ido Schimmel [...] > @@ -980,7 +985,7 @@ static int __ipv6_dev_mc_inc(struct net_device *dev, > return -ENOMEM; > } > > - rcu_assign_pointer(mc->next, idev->mc_list); > + rcu_assign_pointer(mc->next, mc_dereference(idev->mc_list, idev)); > rcu_assign_pointer(idev->mc_list, mc); > > mld_del_delrec(idev, mc); In case you need another version: diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c index aaba4c2aae23..bb1b8957967f 100644 --- a/net/ipv6/mcast.c +++ b/net/ipv6/mcast.c @@ -763,7 +763,7 @@ static void mld_add_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im) psf->sf_crcount = pmc->mca_crcount; } - rcu_assign_pointer(pmc->next, idev->mc_tomb); + rcu_assign_pointer(pmc->next, mc_dereference(idev->mc_tomb, idev)); rcu_assign_pointer(idev->mc_tomb, pmc); }