[PATCH 3/5] idpf: skip getting RX flow rules if vport is NULL during HW reset

When an idpf HW reset is triggered, it clears the vport but does
not clear the netdev held by vport:

    // In idpf_vport_dealloc() called by idpf_init_hard_reset(),
    // idpf_init_hard_reset() sets IDPF_HR_RESET_IN_PROG, so
    // idpf_decfg_netdev() doesn't get called.
    if (!test_bit(IDPF_HR_RESET_IN_PROG, adapter->flags))
        idpf_decfg_netdev(vport);
    // idpf_decfg_netdev() would clear netdev but it isn't called:
    unregister_netdev(vport->netdev);
    free_netdev(vport->netdev);
    vport->netdev = NULL;
    // Later in idpf_init_hard_reset(), the vport is cleared:
    kfree(adapter->vports);
    adapter->vports = NULL;

During an idpf HW reset, when userspace gets RX flow classification
rules of the netdev, the vport associated with the netdev is NULL,
and so a kernel panic would happen:

[ 1466.308592] BUG: kernel NULL pointer dereference, address: 0000000000000032
...
[ 1466.356222] RIP: 0010:idpf_get_rxnfc+0x3b/0x70

This can be reproduced reliably by injecting a TX timeout to cause
an idpf HW reset, and injecting a virtchnl error to cause the HW
reset to fail and retry, while running "ethtool -n" in userspace.

With this patch applied, we see the following error but no kernel
panics anymore:

[  312.476576] idpf 0000:05:00.0 eth1: failed to get rules due to no vport in netdev
Cannot get RX rings: Bad address
rxclass: Cannot get RX class rule count: Bad address
RX classification rule retrieval failed

Signed-off-by: Li Li <redacted>
---
 drivers/net/ethernet/intel/idpf/idpf_ethtool.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/ethernet/intel/idpf/idpf_ethtool.c b/drivers/net/ethernet/intel/idpf/idpf_ethtool.c
index 6a4b630b786c2..c71af85408a29 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_ethtool.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_ethtool.c

@@ -45,6 +44,11 @@ static int idpf_get_rxnfc(struct net_device *netdev, struct ethtool_rxnfc *cmd,
 
 	idpf_vport_ctrl_lock(netdev);
 	vport = idpf_netdev_to_vport(netdev);
+	if (!vport) {
+		netdev_err(netdev, "failed to get rules due to no vport in netdev\n");
+		err = -EFAULT;
+		goto unlock;
+	}
 	vport_config = np->adapter->vport_config[np->vport_idx];
 	user_config = &vport_config->user_config;
 

@@ -85,6 +90,7 @@ static int idpf_get_rxnfc(struct net_device *netdev, struct ethtool_rxnfc *cmd,
 		break;
 	}
 
+unlock:
 	idpf_vport_ctrl_unlock(netdev);
 
 	return err;

-- 
2.52.0.351.gbe84eed79e-goog