The driver calls netif_napi_set_irq() and then calls netif_napi_add(),
which calls netif_napi_add_weight(). At the end of
netif_napi_add_weight() is a call to netif_napi_set_irq(napi, -1), which
clears the previously set napi->irq value. Fix this by calling
netif_napi_set_irq() after calling netif_napi_add().

This was found when reviewing another patch and I have no way to test
this, but the fix seemed relatively straight forward.

Cc: stable@vger.kernel.org
Fixes: bc6107771bb4 ("eth: fbnic: Allocate a netdevice and napi vectors with queues")
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
---
 drivers/net/ethernet/meta/fbnic/fbnic_txrx.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_txrx.c b/drivers/net/ethernet/meta/fbnic/fbnic_txrx.c
index 0ed4c9fff5d8..72f88ae7815f 100644
--- a/drivers/net/ethernet/meta/fbnic/fbnic_txrx.c
+++ b/drivers/net/ethernet/meta/fbnic/fbnic_txrx.c
@@ -1012,14 +1012,14 @@ static int fbnic_alloc_napi_vector(struct fbnic_dev *fbd, struct fbnic_net *fbn,
 	nv->fbd = fbd;
 	nv->v_idx = v_idx;
 
-	/* Record IRQ to NAPI struct */
-	netif_napi_set_irq(&nv->napi,
-			   pci_irq_vector(to_pci_dev(fbd->dev), nv->v_idx));
-
 	/* Tie napi to netdev */
 	list_add(&nv->napis, &fbn->napis);
 	netif_napi_add(fbn->netdev, &nv->napi, fbnic_poll);
 
+	/* Record IRQ to NAPI struct */
+	netif_napi_set_irq(&nv->napi,
+			   pci_irq_vector(to_pci_dev(fbd->dev), nv->v_idx));
+
 	/* Tie nv back to PCIe dev */
 	nv->dev = fbd->dev;
 
-- 
2.17.1

On 12/09/2024 18:49, Brett Creeley wrote:
> The driver calls netif_napi_set_irq() and then calls netif_napi_add(),
> which calls netif_napi_add_weight(). At the end of
> netif_napi_add_weight() is a call to netif_napi_set_irq(napi, -1), which
> clears the previously set napi->irq value. Fix this by calling
> netif_napi_set_irq() after calling netif_napi_add().
> 
> This was found when reviewing another patch and I have no way to test
> this, but the fix seemed relatively straight forward.
> Cc: stable@vger.kernel.org
> Fixes: bc6107771bb4 ("eth: fbnic: Allocate a netdevice and napi vectors with queues")
> Signed-off-by: Brett Creeley <brett.creeley@amd.com>

I agree that irq vector is lost without this patch.

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>

On Thu, Sep 12, 2024 at 10:49:22AM -0700, Brett Creeley wrote:
> The driver calls netif_napi_set_irq() and then calls netif_napi_add(),
> which calls netif_napi_add_weight(). At the end of
> netif_napi_add_weight() is a call to netif_napi_set_irq(napi, -1), which
> clears the previously set napi->irq value. Fix this by calling
> netif_napi_set_irq() after calling netif_napi_add().
> 
> This was found when reviewing another patch and I have no way to test
> this, but the fix seemed relatively straight forward.
> 
> Cc: stable@vger.kernel.org
> Fixes: bc6107771bb4 ("eth: fbnic: Allocate a netdevice and napi vectors with queues")
> Signed-off-by: Brett Creeley <brett.creeley@amd.com>

I agree with your analysis, but I'm not sure if this needs to be
backported to other kernels because:
  - It is not a device that is easily available (currently),
  - The bug is relatively minor

I'm not a maintainer so I'll let those folks decide if this should
be a net-next thing to reduce load on the stable folks.

In any case:

Reviewed-by: Joe Damato <jdamato@fastly.com>