[PATCH 4/5] idpf: skip setting channels 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 changes the netdev channels,
the vport associated with the netdev is NULL, and so a kernel panic
would happen:

[ 2245.795117] BUG: kernel NULL pointer dereference, address: 0000000000000088
...
[ 2245.842720] RIP: 0010:idpf_set_channels+0x40/0x120

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 -L" in userspace.

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

[ 1176.743096] idpf 0000:05:00.0 eth1: channels not changed due to no vport in netdev
netlink error: Bad address

Signed-off-by: Li Li <redacted>
---
 drivers/net/ethernet/intel/idpf/idpf_ethtool.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/intel/idpf/idpf_ethtool.c b/drivers/net/ethernet/intel/idpf/idpf_ethtool.c
index c71af85408a29..1b03528041af4 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_ethtool.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_ethtool.c

@@ -580,6 +579,11 @@ static int idpf_set_channels(struct net_device *netdev,
 
 	idpf_vport_ctrl_lock(netdev);
 	vport = idpf_netdev_to_vport(netdev);
+	if (!vport) {
+		netdev_err(netdev, "channels not changed due to no vport in netdev\n");
+		err = -EFAULT;
+		goto unlock_mutex;
+	}
 
 	idx = vport->idx;
 	vport_config = vport->adapter->vport_config[idx];

-- 
2.52.0.351.gbe84eed79e-goog