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Wed, 6 May 2026 21:13:06 +0000 Message-ID: <7343677e-a652-4770-8cb4-2a938eddaf74@intel.com> Date: Wed, 6 May 2026 14:13:03 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 10/13] ice: fix locking in ice_dcb_rebuild() To: Przemek Kitszel , Andrew Lunn , "David S. Miller" , "Eric Dumazet" , Jakub Kicinski , Paolo Abeni , Piotr Kwapulinski , Aleksandr Loktionov , Arkadiusz Kubalewski , Maciej Fijalkowski , Michal Kubiak , Joshua Hay , Madhu Chittim , Willem de Bruijn , Dave Ertman , Ivan Vecera , Grzegorz Nitka CC: , , Bart Van Assche , , Arpana Arland References: <20260504-jk-iwl-net-2026-05-04-v1-0-a222a88bd962@intel.com> <20260504-jk-iwl-net-2026-05-04-v1-10-a222a88bd962@intel.com> Content-Language: en-US From: Jacob Keller In-Reply-To: <20260504-jk-iwl-net-2026-05-04-v1-10-a222a88bd962@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0295.namprd04.prod.outlook.com (2603:10b6:303:89::30) To SN7PR11MB7592.namprd11.prod.outlook.com (2603:10b6:806:343::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: SN7PR11MB7592:EE_|PH8PR11MB6780:EE_ X-MS-Office365-Filtering-Correlation-Id: 7c2a7be2-c027-43a2-355e-08deabb44482 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016|921020|3023799003|56012099003|18002099003|22082099003; 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The second ice_query_port_ets() > call in ice_dcb_rebuild() is already protected by pf->tc_mutex. > > This also fixes a bug in an error path, as before taking the first > "goto dcb_error" in the function jumped over mutex_lock() to > mutex_unlock(). > > This bug has been detected by the clang thread-safety analyzer. > > Cc: Aleksandr Loktionov > Cc: intel-wired-lan@lists.osuosl.org > Fixes: 242b5e068b25 ("ice: Fix DCB rebuild after reset") > Signed-off-by: Bart Van Assche > Reviewed-by: Aleksandr Loktionov > Reviewed-by: Przemek Kitszel > Tested-by: Arpana Arland > Signed-off-by: Jacob Keller > --- > drivers/net/ethernet/intel/ice/ice_dcb_lib.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ethernet/intel/ice/ice_dcb_lib.c b/drivers/net/ethernet/intel/ice/ice_dcb_lib.c > index 16aa25535152..0bc6dd375687 100644 > --- a/drivers/net/ethernet/intel/ice/ice_dcb_lib.c > +++ b/drivers/net/ethernet/intel/ice/ice_dcb_lib.c > @@ -537,14 +537,14 @@ void ice_dcb_rebuild(struct ice_pf *pf) > struct ice_dcbx_cfg *err_cfg; > int ret; > > + mutex_lock(&pf->tc_mutex); > + > ret = ice_query_port_ets(pf->hw.port_info, &buf, sizeof(buf), NULL); > if (ret) { > dev_err(dev, "Query Port ETS failed\n"); > goto dcb_error; > } > > - mutex_lock(&pf->tc_mutex); > - > if (!pf->hw.port_info->qos_cfg.is_sw_lldp) > ice_cfg_etsrec_defaults(pf->hw.port_info); > > Sashiko thinks there is a problem here: > Does moving mutex_lock(&pf->tc_mutex) to the top of ice_dcb_rebuild() > introduce an AB-BA deadlock with rtnl_lock? > In standard DCB netlink operations, the netlink layer calls into the driver > with rtnl_lock already held, and the driver subsequently acquires > pf->tc_mutex. This establishes a required lock ordering of rtnl_lock > followed by pf->tc_mutex. > With this change, if the first ice_query_port_ets() fails, we take the goto > dcb_error path while already holding pf->tc_mutex. > Looking at the error cleanup path lower down in ice_dcb_rebuild(): > dcb_error: > dev_err(dev, "Disabling DCB until new settings occur\n"); > [ ... ] > ice_pf_dcb_cfg(pf, err_cfg, false); > Because the locked parameter is passed as false, ice_pf_dcb_cfg() will > unconditionally acquire rtnl_lock(). > Does this create a lock inversion (pf->tc_mutex followed by rtnl_lock) > against concurrent DCB netlink operations? This seems like a fully pre-existing error. We already jump to dcb_error else where in the function. I don't know if this locking order really is an ABBA violation (I did not review any of the other flows that take tc_mutex to confirm), but I don't think it should hold this fix. Someone from the ice team will need to investigate and see what the best solution is. I suspect we'll have to take RTNL lock then the tc_mutex and pass true to the ice_pf_dcb_cfg function. Or, better yet, see if this converts to the netdev per-instance lock and we could drop the tc_mutex entirely, relying on netdev_lock? Thanks, Jake