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

[Li Li <boolli@google.com>]

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 <boolli@google.com>
---
 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