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emacs 30.2 From: Petr Machata To: Victor Nogueira CC: , , , , , , , , , , Subject: Re: [PATCH net 1/2] net/sched: ets: Remove drr class from the active list if it changes to strict Date: Tue, 9 Dec 2025 14:42:10 +0100 In-Reply-To: <20251208190125.1868423-1-victor@mojatatu.com> Message-ID: <87ikefwybc.fsf@nvidia.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: rnnvmail202.nvidia.com (10.129.68.7) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS3PEPF000099DA:EE_|LV8PR12MB9155:EE_ X-MS-Office365-Filtering-Correlation-Id: 11f44f5a-a2b0-4600-e749-08de372b4112 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|82310400026|1800799024|36860700013|13003099007; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?NWp6A120122ELK9DseOW48HftR0PhHdK95QfKtn+eJ8KYvlFqbHLrLczZm7m?= =?us-ascii?Q?RK28yk3BsFx7oxPVHajEgyqO8OzYCLzyEeXm4e4FK/YQC34F+8SYmit2zk4k?= =?us-ascii?Q?I077qipSYf4E9uSPoUw67AS3BU3x9Gd5HuHjx2n0PWD83mCAEK1d/2CZLrr5?= =?us-ascii?Q?SSrxnHEzMSrxGI9+kN/TIvApDLrYylhuftjX8wR5UlHl1gLmgfZzKcm/nGdy?= =?us-ascii?Q?k4nEUTVm9NReKPZhevVaEqwPy1cijg/kmfmvHKpgg2GUvAFZyyhBPjH9tWqg?= =?us-ascii?Q?vUdXuDxfxmOuK19h1GTKliV9BSLXztoW2jFjDbgvRs3fqqpRaBZHI4rzrZX1?= =?us-ascii?Q?3KtgmvhdhSLVV6Dc9CUzMvnmykjnE1vJGM2UgIdzkPurfkO3sS/PXqQZV1a4?= =?us-ascii?Q?es4XmiQsZ4Hfl+sLMRDAm9K5hW4K2WNW4WIum1ra8OpZHIGPPboSuFgwZtLC?= =?us-ascii?Q?72spM7VFtF8N4Y0sDt90iGbh/IUjuCM0MO1GEJYH7Ig2mVRulXHLy5XS4RjE?= =?us-ascii?Q?vAJEIphJ08zv5Qn+aodvl9Tj4nc5O8D2Dj8HQlWYbdFDoQkAK9k3/kaPlXKy?= =?us-ascii?Q?FsYQZaVbg2b+l6WTZ5/l192nyjVwEkq+XlL0nWYp33/yDvASHSPqbB2hjRVN?= =?us-ascii?Q?alznPV6eIvwIzKtFGhsNgdKvEeazs3hV8dJQ94uGtsc1rqbf7BACMiUi59AB?= =?us-ascii?Q?eLMV5KOwkr0DLLD6EEbYkFQDIhtLjC2g/wb9CtKtR1M6x9lmNnPmm6ZQQeNv?= =?us-ascii?Q?Ri69aj18PMRmre5lkVZbvooLrCGy4bIOLdEb/xvKvYaBnuUK03MJ0/Zgvmnp?= =?us-ascii?Q?016cN0OsBRMq3+afJz4KNnP2IcwHVslh1tno/73IsROAsNTbpQ1n2o4i/Wpa?= =?us-ascii?Q?Xzs0Qpf2xYLifrXQHcz6aQpFieuE8AMyXYmKdGxypSBqoMmiTO1QrpLLkzZd?= =?us-ascii?Q?cf3gp2nsztcPv65tzTS9FSL7PcqGIvfHVVKIwx0ayKWSPRHkscqpQInTnU4x?= =?us-ascii?Q?rniyitrlRskx1XWOpmhdOlz1OUU/Cq232CdlZ8GsD+qge9N9QPP+JeJFBi4O?= =?us-ascii?Q?knKgcK4hKbGan7hMYfJAeSu3LhCGTSxhQ9avIQ9EVmQ6CgLgZVcp5nKjpyj/?= =?us-ascii?Q?IKd0eNkjz2h42io5jcr1w1crNO2nIkzPsKDJMeNbdUWOMblnZ1iH8KgeI9nV?= =?us-ascii?Q?/kORFKW5uObrNmX4RrdzYWzx5ZwuLjzX4u+sm9HcHeHLrEDNqLbLG9XAoJ+H?= =?us-ascii?Q?lk7QfprBucYIQ4s9t0zMQ1wcjVZsE31RsZiOPUAwBMBiw+2SrY+p0r63ihzt?= =?us-ascii?Q?Z775vf6o0+rC+RuJXORlfoyBDRqftp/kruF3HMCT09d3TfXpPCD0ZKzfTIXo?= =?us-ascii?Q?5P6XzrQBRcp0tk5k/gTF6y7SAoGXpaT3qTQdUTyEpCkbTSoaQ+A5w5SA+d73?= =?us-ascii?Q?NmUF7fOw3pjIRnbL0kfv+yJKTLqSmMf9e8bJqmNzAIJ26nCPQjaquzKjasJy?= =?us-ascii?Q?tiiLhOdxBAKHCuDSt/aJgsKFs3xZx9TZT2pazyGA1Pw2PEtzfb0tyH2mOAI3?= =?us-ascii?Q?JHV2dNRgDZHSBnnNSoI=3D?= X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230040)(7416014)(376014)(82310400026)(1800799024)(36860700013)(13003099007);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Dec 2025 14:00:04.6620 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 11f44f5a-a2b0-4600-e749-08de372b4112 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DS3PEPF000099DA.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR12MB9155 Victor Nogueira writes: > Whenever a user issues an ets qdisc change command, transforming a > drr class into a strict one, the ets code isn't checking whether that > class was in the active list and removing it. This means that, if a > user changes a strict class (which was in the active list) back to a drr > one, that class will be added twice to the active list [1]. > > Doing so with the following commands: > > tc qdisc add dev lo root handle 1: ets bands 2 strict 1 > tc qdisc add dev lo parent 1:2 handle 20: \ > tbf rate 8bit burst 100b latency 1s > tc filter add dev lo parent 1: basic classid 1:2 > ping -c1 -W0.01 -s 56 127.0.0.1 > tc qdisc change dev lo root handle 1: ets bands 2 strict 2 > tc qdisc change dev lo root handle 1: ets bands 2 strict 1 > ping -c1 -W0.01 -s 56 127.0.0.1 > > Will trigger the following splat with list debug turned on: > > [ 59.279014][ T365] ------------[ cut here ]------------ > [ 59.279452][ T365] list_add double add: new=ffff88801d60e350, prev=ffff88801d60e350, next=ffff88801d60e2c0. > [ 59.280153][ T365] WARNING: CPU: 3 PID: 365 at lib/list_debug.c:35 __list_add_valid_or_report+0x17f/0x220 > [ 59.280860][ T365] Modules linked in: > [ 59.281165][ T365] CPU: 3 UID: 0 PID: 365 Comm: tc Not tainted 6.18.0-rc7-00105-g7e9f13163c13-dirty #239 PREEMPT(voluntary) > [ 59.281977][ T365] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > [ 59.282391][ T365] RIP: 0010:__list_add_valid_or_report+0x17f/0x220 > [ 59.282842][ T365] Code: 89 c6 e8 d4 b7 0d ff 90 0f 0b 90 90 31 c0 e9 31 ff ff ff 90 48 c7 c7 e0 a0 22 9f 48 89 f2 48 89 c1 4c 89 c6 e8 b2 b7 0d ff 90 <0f> 0b 90 90 31 c0 e9 0f ff ff ff 48 89 f7 48 89 44 24 10 4c 89 44 > ... > [ 59.288812][ T365] Call Trace: > [ 59.289056][ T365] > [ 59.289224][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 59.289546][ T365] ets_qdisc_change+0xd2b/0x1e80 > [ 59.289891][ T365] ? __lock_acquire+0x7e7/0x1be0 > [ 59.290223][ T365] ? __pfx_ets_qdisc_change+0x10/0x10 > [ 59.290546][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 59.290898][ T365] ? __mutex_trylock_common+0xda/0x240 > [ 59.291228][ T365] ? __pfx___mutex_trylock_common+0x10/0x10 > [ 59.291655][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 59.291993][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 59.292313][ T365] ? trace_contention_end+0xc8/0x110 > [ 59.292656][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 59.293022][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 59.293351][ T365] tc_modify_qdisc+0x63a/0x1cf0 > > Fix this by always checking and removing an ets class from the active list > when changing it to strict. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/tree/net/sched/sch_ets.c?id=ce052b9402e461a9aded599f5b47e76bc727f7de#n663 > > Fixes: cd9b50adc6bb9 ("net/sched: ets: fix crash when flipping from 'strict' to 'quantum'") > Acked-by: Jamal Hadi Salim > Signed-off-by: Victor Nogueira Reviewed-by: Petr Machata