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    SubjectRe: unregister_netdevice: waiting for DEV to become free (2)
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    On 4/27/19 9:22 PM, Tetsuo Handa wrote:
    > On 2019/04/28 8:52, Eric Dumazet wrote:
    >> On 4/27/19 3:33 PM, Tetsuo Handa wrote:
    >>>
    >>> I'm waiting for davem why it is safe to move the dst entry from
    >>> "a device to unregister" to "a loopback device in that namespace".
    >>> I'm waiting for an explanation how the dst entry which was moved to
    >>> "a loopback device in that namespace" is released (i.e. what the
    >>> expected shutdown sequence is).
    >>
    >> The most probable explanation is that we make sure the loopback device
    >> is the last one to be dismantled at netns deletion,
    >> and this would obviously happen after all dst have been released.
    >>
    >
    > rt_flush_dev() becomes a no-op if "dev" == "a loopback device in that
    > namespace". And according to debug printk(), rt_flush_dev() is called
    > on "a loopback device in that namespace" itself.
    >

    This is the design yes. We can not let a dst having a pointer to some garbage memory.
    (since we are going to free it very soon)

    dst can be long lived objects. netdev (but loopback) are not.

    > If "a loopback device in that namespace" is the last "one" (== "a network
    > device in that namespace" ?), which shutdown sequence should have called
    > dev_put("a loopback device in that namespace") before unregistration of
    > "a loopback device in that namespace" starts?

    You'll have to study all the netdev notifiers to answer this question.
    They are many of them, and they have a priority to let them run in a given order.

    >
    > Since I'm not a netdev person, I appreciate if you can explain
    > that shutdown sequence using a flow chart.

    I am a netdev person, but I have no time to explain this at this moment.

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