Home/ Questions/Q 8779193
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-13T19:43:27+00:00

is it required to unlock net_device structure before calling free_netdev? The code I encountered

  • 0

is it required to unlock net_device structure before calling free_netdev? The code I encountered does the following:

static void delete_dev(struct net_device *dev)
{
   ASSERT_RTNL();
   ...
   unregister_netdevice(dev);
   ...
   rtnl_unlock();
   free_netdev(dev);
   rtnl_lock();
}

int foo()
{
   struct net_device *dev;

   rtnl_lock();
   ...
   delete_dev(dev);
   rtnl_unlock();
   return 0;
}

Is this the right way to do the things? Thanks.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    You should not unlock-lock rtnl one more time.

    Here is why: there is not a word in Network Drivers API in free_netdev section about lock required. Nevertheless, unregister_netdevice requires lock to be held and it has been wrapped in API in unregister_netdev function, which is stated in the document.

    Anyway, if you look into some popular driver’s sources, e1000e for example, you will see this:

    6432 static void __devexit e1000_remove(struct pci_dev *pdev)
6433 {
...
6459         unregister_netdev(netdev);
6460 
6461         if (pci_dev_run_wake(pdev))
6462                 pm_runtime_get_noresume(&pdev->dev);
6463 
6464         /*
6465          * Release control of h/w to f/w.  If f/w is AMT enabled, this
6466          * would have already happened in close and is redundant.
6467          */
6468         e1000e_release_hw_control(adapter);
6469 
6470         e1000e_reset_interrupt_capability(adapter);
6471         kfree(adapter->tx_ring);
6472         kfree(adapter->rx_ring);
6473 
6474         iounmap(adapter->hw.hw_addr);
6475         if (adapter->hw.flash_address)
6476                 iounmap(adapter->hw.flash_address);
6477         pci_release_selected_regions(pdev,
6478                                      pci_select_bars(pdev, IORESOURCE_MEM));
6479 
6480         free_netdev(netdev);
6481 
6482         /* AER disable */
6483         pci_disable_pcie_error_reporting(pdev);
6484 
6485         pci_disable_device(pdev);
6486 }

    As you can see, there is no unlock-lock taken.

    Moreover, they use unregister_netdev function so that it would only be locked inside unregister_netdevice itself, and all dozens of deinitialinizations there would go outside the lock. Therefore, consider using simple unregister_netdev as they(netdev kernel developers) recommend in comments to it’s source, if you think you can afford that.

    • 0