netdev - Re: [Ipw2100-devel] ipw2100: race between isr_indicate

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Date:	Fri, 27 Feb 2009 08:55:39 +0800
From:	Zhu Yi <yi.zhu@...el.com>
To:	Helmut Schaa <helmut.schaa@...glemail.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	Jouni Malinen <j@...fi>
Subject: Re: [Ipw2100-devel] ipw2100: race between isr_indicate_associated
 and rx path

On Wed, 2009-02-25 at 20:39 +0800, Helmut Schaa wrote:
> Argh! Just found out why dev_activate is called such late after
> netif_carrier_on:
> 
> ipw2100 calls netif_carrier_on followed by netif_wake_queue when the
> driver
> moves from associating to associated state. netif_carrier_on will then
> call linkwatch_fire_event. However the carrier_on event is not treated
> as
> urgent and as such the event is delayed (and thus dev_activate too).
> 
> An event is considered urgent if the netdev is running, has a carrier
> _and_ any of the TX qdiscs changed. Since ipw2100 first calls
> carrier_on,
> the last condition is not met and thus the event is not considered
> urgent and gets delayed.

Calling netif_wake_queue() before netif_carrier_on() is not correct in
semantics. Even it works, it looks like a workaround hack. I still think
making a sync version of netif_carrier_on is the way to go.

> Just changing the order to first wake up the queues followed by the
> carrier_on results in an urgent event. I ran a few tests with that
> change
> (+ frame buffering patch) and wasn't able to trigger the race again.
> 
> I'll fold that into the frame buffer patch and send it to
> ipw2100-devel
> once I finished the tests.

Sounds good.

Thanks,
-yi

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