netdev - problem with noop and pfifo

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Message-ID: <81C3A93C17462B4BBD7E272753C105791FB3639775@EXDCVYMBSTM005.EQ1STM.local>
Date:	Thu, 19 Jan 2012 13:47:33 +0100
From:	Hemant-vilas RAMDASI <hemant.ramdasi@...ricsson.com>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>
Subject: problem with noop and pfifo_fast Qdisc switching

Hi,

I have a situation where one of important message (phonet pipe message) gets dropped because of 'noop' Qdisc.
This situation mostly happens when coming out of sleep and there is a message to send.
What I have observed is this.
In normal case the qdisc used id pfifo_fast. When CPU goes to sleep, it changes the qdisc to noop.
When CPU wakes up (because of a message from lower layers), phonet tries to send a control packet to driver and finds qdisc is still 'noop'. 
Because the concerned message is a control message, this packet drop is creating deadlock situation.

How the switch between pfifo_fast and noop is handled? Is this something solved in 3.0?
We are running a older version of kernel (2.6.35 based).

Thanks,
Hemant

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