Re: Re: LLTX and netif_stop_queue

[Roland Dreier <roland@topspin.com>]

    Roland> I may be missing something, but it seems to me that we get
    Roland> all of the benefits of LLTX by just documenting that
    Roland> device drivers can use the xmit_lock member of struct
    Roland> net_device to synchronize other parts of the driver
    Roland> against hard_start_xmit.  I guess the driver also should
    Roland> set xmit_lock_owner to -1 after it acquires xmit_lock.

Thinking about this a little more, I realize that there's no reason
for the driver to set xmit_lock_owner -- if the driver is able to
acquire the lock, then xmit_lock_owner will already be -1.

So it seems LLTX can be replaced by just having drivers use
net_device.xmit_lock instead of their own private tx_lock.  Assuming
this works (and I don't see anything wrong with it) then this seems
like a pretty nice solution: we remove some code from the networking
core and get rid of all the "trylock" logic in driver's hard_start_xmit.

 - Roland