RE: [PATCH iwl-net 1/3] ice: avoid RTNL deadlock when notifying the RDMA auxiliary driver

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Petr Oros <poros@xxxxxxxxxx>
> Sent: Monday, October 19, 2026 8:53 AM
> To: netdev@xxxxxxxxxxxxxxx
> Cc: Oros, Petr <poros@xxxxxxxxxx>; Nguyen, Anthony L
> <anthony.l.nguyen@xxxxxxxxx>; Kitszel, Przemyslaw
> <przemyslaw.kitszel@xxxxxxxxx>; Andrew Lunn <andrew+netdev@xxxxxxx>;
> David S . Miller <davem@xxxxxxxxxxxxx>; Eric Dumazet
> <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni
> <pabeni@xxxxxxxxxx>; Ertman, David M <david.m.ertman@xxxxxxxxx>; Shiraz
> Saleem <shiraz.saleem@xxxxxxxxx>; Leon Romanovsky <leon@xxxxxxxxxx>;
> Maziarz, Kamil <kamil.maziarz@xxxxxxxxx>; Rafal Rogalski
> <rafalx.rogalski@xxxxxxxxx>; Loktionov, Aleksandr
> <aleksandr.loktionov@xxxxxxxxx>; Schmidt, Michal <mschmidt@xxxxxxxxxx>;
> linux-rdma@xxxxxxxxxxxxxxx; intel-wired-lan@xxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; Sebastian Andrzej
> Siewior <bigeasy@xxxxxxxxxxxxx>; Clark Williams <clrkwllms@xxxxxxxxxx>;
> Steven Rostedt <rostedt@xxxxxxxxxxx>; Mateusz Palczewski
> <mateusz.palczewski@xxxxxxxxx>; linux-rt-devel@xxxxxxxxxxxxxxx
> Subject: [PATCH iwl-net 1/3] ice: avoid RTNL deadlock when notifying the
> RDMA auxiliary driver
> 
> ice_send_event_to_aux() blocks on the auxiliary device lock, and the
> dcbnl callers reach it with the RTNL lock held. The RDMA auxiliary probe
> takes the two in the opposite order, because __driver_attach() holds the
> auxiliary device lock across ib_register_device(), which needs the RTNL
> lock:
> 
>   systemd-udevd   state:D
>     really_probe                  <- holds device_lock(&adev->dev)
>     icrdma_probe
>     irdma_ib_register_device
>     ib_register_device
>     setup_device
>     irdma_roce_port_immutable
>     ib_query_port
>     irdma_query_port
>     ib_get_eth_speed              <- blocks on rtnl_lock()
> 
>   lldpad          state:D
>     rtnetlink_rcv_msg             <- holds rtnl_lock()
>     dcb_doit
>     dcbnl_ieee_set
>     ice_dcbnl_setets
>     ice_pf_dcb_cfg
>     ice_send_event_to_aux         <- blocks on device_lock(&adev->dev)
> 
> Everything else that needs the RTNL lock piles up behind lldpad and the
> boot never completes. The probe side cannot be changed, so use
> device_trylock() and report whether the event reached the driver.
> 
> IIDC_RDMA_EVENT_BEFORE_TC_CHANGE has to arrive before the traffic
> classes change, so ice_pf_dcb_cfg() refuses the request with -EBUSY
> rather than run it behind the RDMA driver's back. The critical error and
> MTU change events are sent from the service task, which consumes their
> pending bits before sending, so those are re-armed instead.
> AFTER_TC_CHANGE keeps its fire and forget behaviour, it can be neither
> refused, the hardware has already changed, nor deferred, every lock that
> would serialise a deferred delivery against the dcbnl callers forms
> another cycle.
> 
> Fixes: 348048e724a0 ("ice: Implement iidc operations")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Petr Oros <poros@xxxxxxxxxx>
> ---
>  drivers/net/ethernet/intel/ice/ice_dcb_lib.c |  9 ++++++++-
>  drivers/net/ethernet/intel/ice/ice_idc.c     | 20 ++++++++++++++++----
>  drivers/net/ethernet/intel/ice/ice_idc_int.h |  2 +-
>  drivers/net/ethernet/intel/ice/ice_main.c    | 16 ++++++++++++----
>  4 files changed, 37 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> b/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> index 0bc6dd37568792..2022b46c990cb2 100644
> --- a/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> +++ b/drivers/net/ethernet/intel/ice/ice_dcb_lib.c
> @@ -355,8 +355,10 @@ int ice_pf_dcb_cfg(struct ice_pf *pf, struct
> ice_dcbx_cfg *new_cfg, bool locked)
>  	struct iidc_rdma_event *event;
>  	int ret = ICE_DCB_NO_HW_CHG;
>  	struct ice_vsi *pf_vsi;
> +	bool dcb_ena;
> 
>  	curr_cfg = &pf->hw.port_info->qos_cfg.local_dcbx_cfg;
> +	dcb_ena = test_bit(ICE_FLAG_DCB_ENA, pf->flags);
> 
>  	/* FW does not care if change happened */
>  	if (!pf->hw.port_info->qos_cfg.is_sw_lldp)
> @@ -406,7 +408,12 @@ int ice_pf_dcb_cfg(struct ice_pf *pf, struct
> ice_dcbx_cfg *new_cfg, bool locked)
>  	}
> 
>  	set_bit(IIDC_RDMA_EVENT_BEFORE_TC_CHANGE, event->type);
> -	ice_send_event_to_aux(pf, event);
> +	if (!ice_send_event_to_aux(pf, event)) {
> +		assign_bit(ICE_FLAG_DCB_ENA, pf->flags, dcb_ena);
> +		kfree(event);
> +		ret = -EBUSY;
-EBUSY doesn't match to any ICE_DCB_* constant, are you sure you tested this case?
It looks like it will be processed like ICE_DCB_NO_HW_CHG i.e. no change needed, isn't it?


> +		goto free_cfg;
> +	}
>  	kfree(event);
> 
>  	/* avoid race conditions by holding the lock while disabling and
> diff --git a/drivers/net/ethernet/intel/ice/ice_idc.c
> b/drivers/net/ethernet/intel/ice/ice_idc.c
> index 102d63c3018b1f..7fd35ce966ea65 100644
> --- a/drivers/net/ethernet/intel/ice/ice_idc.c
> +++ b/drivers/net/ethernet/intel/ice/ice_idc.c
> @@ -34,30 +34,42 @@ ice_get_auxiliary_drv(struct iidc_rdma_core_dev_info
> *cdev)
>   * ice_send_event_to_aux - send event to RDMA AUX driver
>   * @pf: pointer to PF struct
>   * @event: event struct

...

>  			kfree(event);
>  		}
>  	}
> --
> 2.56.0