Subject: Re: [PATCH net] sfc: fix XDP queues mode with legacy IRQ

From: Martin Habets <[email-masked]>
Date: Thu, 15 Jun 2023 09:00:56 +0100

On Tue, Jun 13, 2023 at 03:38:54PM +0200, Íñigo Huguet wrote:
> In systems without MSI-X capabilities, xdp_txq_queues_mode is calculated
> in efx_allocate_msix_channels, but when enabling MSI-X fails, it was not
> changed to a proper default value. This was leading to the driver
> thinking that it has dedicated XDP queues, when it didn't.
> 
> Fix it by setting xdp_txq_queues_mode to the correct value if the driver
> fallbacks to MSI or legacy IRQ mode. The correct value is
> EFX_XDP_TX_QUEUES_BORROWED because there are not XDP dedicated queues.

Small typo: not should be no.

> 
> The issue can be easily visible if the kernel is started with pci=nomsi,
> then a call trace is shown. It is not shown only with sfc's modparam
> interrupt_mode=2. Call trace example:
>  WARNING: CPU: 2 PID: 663 at drivers/net/ethernet/sfc/efx_channels.c:828 efx_set_xdp_channels+0x124/0x260 [sfc]
>  [...skip...]
>  Call Trace:
>   <TASK>
>   efx_set_channels+0x5c/0xc0 [sfc]
>   efx_probe_nic+0x9b/0x15a [sfc]
>   efx_probe_all+0x10/0x1a2 [sfc]
>   efx_pci_probe_main+0x12/0x156 [sfc]
>   efx_pci_probe_post_io+0x18/0x103 [sfc]
>   efx_pci_probe.cold+0x154/0x257 [sfc]
>   local_pci_probe+0x42/0x80
> 
> Fixes: 6215b608a8c4 ("sfc: last resort fallback for lack of xdp tx queues")
> Reported-by: Yanghang Liu <[email-masked]>
> Signed-off-by: Íñigo Huguet <[email-masked]>

Acked-by: Martin Habets <[email-masked]>

> ---
>  drivers/net/ethernet/sfc/efx_channels.c       | 2 ++
>  drivers/net/ethernet/sfc/siena/efx_channels.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/net/ethernet/sfc/efx_channels.c b/drivers/net/ethernet/sfc/efx_channels.c
> index fcea3ea809d7..41b33a75333c 100644
> --- a/drivers/net/ethernet/sfc/efx_channels.c
> +++ b/drivers/net/ethernet/sfc/efx_channels.c
> @@ -301,6 +301,7 @@ int efx_probe_interrupts(struct efx_nic *efx)
>  		efx->tx_channel_offset = 0;
>  		efx->n_xdp_channels = 0;
>  		efx->xdp_channel_offset = efx->n_channels;
> +		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_BORROWED;
>  		rc = pci_enable_msi(efx->pci_dev);
>  		if (rc == 0) {
>  			efx_get_channel(efx, 0)->irq = efx->pci_dev->irq;
> @@ -322,6 +323,7 @@ int efx_probe_interrupts(struct efx_nic *efx)
>  		efx->tx_channel_offset = efx_separate_tx_channels ? 1 : 0;
>  		efx->n_xdp_channels = 0;
>  		efx->xdp_channel_offset = efx->n_channels;
> +		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_BORROWED;
>  		efx->legacy_irq = efx->pci_dev->irq;
>  	}
>  
> diff --git a/drivers/net/ethernet/sfc/siena/efx_channels.c b/drivers/net/ethernet/sfc/siena/efx_channels.c
> index 06ed74994e36..1776f7f8a7a9 100644
> --- a/drivers/net/ethernet/sfc/siena/efx_channels.c
> +++ b/drivers/net/ethernet/sfc/siena/efx_channels.c
> @@ -302,6 +302,7 @@ int efx_siena_probe_interrupts(struct efx_nic *efx)
>  		efx->tx_channel_offset = 0;
>  		efx->n_xdp_channels = 0;
>  		efx->xdp_channel_offset = efx->n_channels;
> +		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_BORROWED;
>  		rc = pci_enable_msi(efx->pci_dev);
>  		if (rc == 0) {
>  			efx_get_channel(efx, 0)->irq = efx->pci_dev->irq;
> @@ -323,6 +324,7 @@ int efx_siena_probe_interrupts(struct efx_nic *efx)
>  		efx->tx_channel_offset = efx_siena_separate_tx_channels ? 1 : 0;
>  		efx->n_xdp_channels = 0;
>  		efx->xdp_channel_offset = efx->n_channels;
> +		efx->xdp_txq_queues_mode = EFX_XDP_TX_QUEUES_BORROWED;
>  		efx->legacy_irq = efx->pci_dev->irq;
>  	}
>  
> -- 
> 2.40.1