Re: [PATCH v3 iwl-net] i40e: keep q_vectors array in sync with channel count changes

[Simon Horman <horms@kernel.org>]

On Tue, May 19, 2026 at 12:56:38PM +0200, Maciej Fijalkowski wrote:
> For the main VSI, i40e_set_num_rings_in_vsi() always derives
> num_q_vectors from pf->num_lan_msix. At the same time, ethtool -L stores
> the user requested channel count in vsi->req_queue_pairs and the queue
> setup path uses that value for the effective number of queue pairs.
> 
> This leaves queue and vector counts out of sync after shrinking channel
> count via ethtool -L. The active queue configuration is reduced, but the
> VSI still keeps the full PF-sized q_vector topology.
> 
> That mismatch breaks reconfiguration flows which rely on vector/NAPI
> state matching the effective channel configuration. In particular,
> toggling /sys/class/net/<dev>/threaded after reducing the channel count
> can hang, and later channel-count changes can fail because VSI reinit
> does not rebuild q_vectors to match the new vector count.
> 
> Fix this by making the main VSI num_q_vectors follow the effective
> requested channel count, capped by the available MSI-X vectors. Update
> i40e_vsi_reinit_setup() to rebuild q_vectors during VSI reinit so the
> vector topology is refreshed together with the ring arrays when channel
> count changes.
> 
> Keep alloc_queue_pairs unchanged and based on pf->num_lan_qps so the VSI
> retains its full queue capacity.
> 
> Selftest napi_threaded.py was originally used when Jakub reported hang
> on /sys/class/net/<dev>/threaded toggle. In order to make it pass on
> i40e, use persistent NAPI configuration for q_vector NAPIs so NAPI
> identity and threaded settings survive q_vector reallocation across
> channel-count changes. This is achieved by using netif_napi_add_config()
> when configuring q_vectors.
> 
> $ export NETIF=ens259f1np1
> $ sudo -E env PATH="$PATH" ./tools/testing/selftests/drivers/net/napi_threaded.py
> TAP version 13
> 1..3
> ok 1 napi_threaded.napi_init
> ok 2 napi_threaded.change_num_queues
> ok 3 napi_threaded.enable_dev_threaded_disable_napi_threaded
> Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Reported-by: Jakub Kicinski <kuba@kernel.org>
> Closes: https://lore.kernel.org/intel-wired-lan/20260316133100.6054a11f@kernel.org/
> Fixes: d2a69fefd756 ("i40e: Fix changing previously set num_queue_pairs for PFs")
> Reviewed-by: Simon Horman <horms@kernel.org>
> Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> ---
> v3:
> - address UAF when ring arrays where freed before q_vector's ring
>   containers (Sashiko, Jacob)
> - remove bool params from alloc/free array routines (Simon)
> v2:
> - NULL vsi->tx_rings in i40e_vsi_alloc_arrays() (Sashiko)

I notice that there is an AI review of this patch available on sashiko.dev.
However, I believe that flags a pre-existing problem that is orthogonal to
this patch. o I do no think that review should block progress of this
patch but rather be looked at in the context of possible follow-up.