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Thu, 16 Apr 2026 20:46:54 +0000 Message-ID: <70776680-1b60-4898-b9cd-bcc48abaac76@intel.com> Date: Thu, 16 Apr 2026 13:46:52 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 10/13] i40e: fix napi_enable/disable skipping ringless q_vectors To: Przemek Kitszel , Andrew Lunn , "David S. Miller" , "Eric Dumazet" , Jakub Kicinski , Paolo Abeni CC: , Aleksandr Loktionov , , Sunitha Mekala , Maciej Fijalkowski References: <20260414-iwl-net-submission-2026-04-14-v1-0-852f38e7da39@intel.com> <20260414-iwl-net-submission-2026-04-14-v1-10-852f38e7da39@intel.com> <6cc3c5b2-fb71-42a4-8d5b-57cd85de2f02@intel.com> Content-Language: en-US From: Jacob Keller In-Reply-To: <6cc3c5b2-fb71-42a4-8d5b-57cd85de2f02@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4P221CA0018.NAMP221.PROD.OUTLOOK.COM (2603:10b6:303:8b::23) To PH0PR11MB7588.namprd11.prod.outlook.com (2603:10b6:510:28b::16) 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: PH0PR11MB7588:EE_|DS0PR11MB7408:EE_ X-MS-Office365-Filtering-Correlation-Id: bdf6b71a-c83e-49c5-e309-08de9bf94aee X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 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X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 7AF03pZBp0UxZdq1JHlIXdvqzcZsfk5lFBF+GiZlEJ4Jr8RpLpGTcFVUZdEeIZXgkBS5fY6ewbWAMqhEBHzpUeVRjoAkwxuxetyPDzreW98= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR11MB7408 X-OriginatorOrg: intel.com On 4/15/2026 9:20 PM, Przemek Kitszel wrote: > On 4/15/26 07:48, Jacob Keller wrote: >> From: Aleksandr Loktionov >> >> After ethtool -L reduces the queue count, i40e_napi_disable_all() sets >> NAPI_STATE_SCHED on all q_vectors, then i40e_vsi_map_rings_to_vectors() >> clears ring pointers on the excess ones.  i40e_napi_enable_all() skips >> those with: >> >>     if (q_vector->rx.ring || q_vector->tx.ring) >>         napi_enable(&q_vector->napi); >> >> leaving them on dev->napi_list with NAPI_STATE_SCHED permanently set. >> >> Writing to /sys/class/net//threaded calls napi_stop_kthread() >> on every entry in dev->napi_list.  The function loops on msleep(20) >> waiting for NAPI_STATE_SCHED to clear -- which never happens for the >> stale q_vectors.  The task hangs in D state forever; a concurrent write >> deadlocks on dev->lock held by the first. >> >> Commit 13a8cd191a2b ("i40e: Do not enable NAPI on q_vectors that have no >> rings") added the guard to prevent a divide-by-zero in i40e_napi_poll() >> when epoll busy-poll iterated all device NAPIs (4.x era). Since >> 7adc3d57fe2b ("net: Introduce preferred busy-polling"), from v5.11, >> napi_busy_loop() polls by napi_id keyed to the socket, so ringless >> q_vectors are never selected.  i40e_msix_clean_rings() also independently >> avoids scheduling NAPI for them.  The guard is safe to remove. >> >> Add an early return in i40e_napi_poll() for num_ringpairs == 0 so the >> function is self-defending against a NULL tx.ring dereference at the >> WB_ON_ITR check, should the NAPI ever fire through an unexpected path. >> >> Reported-by: Jakub Kicinski >> Closes: https://lore.kernel.org/intel-wired- >> lan/20260316133100.6054a11f@kernel.org/ > > Maciej developed a better fix for the problem, and he explicitly asked > to not include this patch. Please drop it from this series. > > Maciej's fix: > https://lore.kernel.org/intel-wired-lan/20260414121405.631092-1- > maciej.fijalkowski@intel.com/T/#u > > ask for reject: > https://lore.kernel.org/intel-wired-lan/ > PH0PR11MB75223C8A00C3183C5082A096A0252@PH0PR11MB7522.namprd11.prod.outlook.com/T/#mbac55f7219d7855a2e5d1527904b2da43ad080cb > Ugh, sorry for failing to notice this when batching this series up :( Thanks, Jake