Re: [Xen-devel] [PATCH] xen-netfront: set real_num_tx_queues to zreo avoid to trigger BUG_ON

[David Miller <davem@xxxxxxxxxxxxx>]

From: Gonglei <arei.gonglei@xxxxxxxxxx>
Date: Sat, 20 Feb 2016 09:27:26 +0800

> It's possible for a race condition to exist between xennet_open() and
> talk_to_netback(). After invoking netfront_probe() then other
> threads or processes invoke xennet_open (such as NetworkManager)
> immediately may trigger BUG_ON(). Besides, we also should reset
> real_num_tx_queues in xennet_destroy_queues().

One should really never invoke register_netdev() until the device is
%100 fully initialized.

This means you cannot call register_netdev() until it is completely
legal to invoke your ->open() method.

And I think that is what the real problem is here.

If you follow the correct rules for ordering wrt. register_netdev()
there are no "races".  Because ->open() must be legally invokable
from the exact moment you call register_netdev().

I'm not applying this, as it really sounds like the fundamental issue
is the order in which the xen-netfront private data is initialized
or setup before being registered.

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