The commit c23d92b8 ("igb: Teardown SR-IOV before
unregister_netdev()") places the unregister_netdev() call after the
igb_disable_sriov() call to avoid functionality issue.

However, it introduces several race conditions when detaching a device.
For example, when .remove() is called, the below interleaving leads to
use-after-free.

 (FREE from device detaching)      |   (USE from netdev core)
igb_remove                         |  igb_ndo_get_vf_config
 igb_disable_sriov                 |  vf >= adapter->vfs_allocated_count?
  kfree(adapter->vf_data)          |
  adapter->vfs_allocated_count = 0 |
                                   |    memcpy(... adapter->vf_data[vf]

Moreover, the igb_disable_sriov() also suffers from data race with the
requests from VF driver.

 (FREE from device detaching)      |   (USE from requests)
igb_remove                         |  igb_msix_other
 igb_disable_sriov                 |   igb_msg_task
  kfree(adapter->vf_data)          |    vf < adapter->vfs_allocated_count
  adapter->vfs_allocated_count = 0 |

To this end, this commit first eliminates the data races from netdev
core by using rtnl_lock (similar to commit 71947923 ("dpaa2-eth: add
MAC/PHY support through phylink")). And then adds a spinlock to
eliminate races from driver requests. (similar to commit 1e53834c
("ixgbe: Add locking to prevent panic when setting sriov_numvfs to zero")

Fixes: c23d92b8 ("igb: Teardown SR-IOV before unregister_netdev()")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20220817184921.735244-1-anthony.l.nguyen@intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>