netdev - Re: [PATCH] net/fec: fix link/queue interaction, wake queue iff link is up

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Message-Id: <20101006.141540.260064338.davem@davemloft.net>
Date:	Wed, 06 Oct 2010 14:15:40 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	oskar@...utronix.de
Cc:	netdev@...r.kernel.org, dan@...eddedalley.com,
	bigeasy@...utronix.de, hjk@...utronix.de
Subject: Re: [PATCH] net/fec: fix link/queue interaction, wake queue iff
 link is up

From: Oskar Schirmer <oskar@...utronix.de>
Date: Wed,  6 Oct 2010 13:31:58 +0200

> with hardware slow in negotiation, the system did freeze
> while trying to mount root on nfs at boot time.
> 
> while the driver did report being busy when the link is down
> or no transmission buffers are available, it did not stop the
> queue, causing instant retries. furthermore, transmission being
> triggered with link down was caused by unconditional queue
> wakes, especially on timeouts.
> 
> now, wake queue only iff link is up and transmission
> buffers are available, and dont forget to wake queue
> when link has been adjusted. next, add stop queue notification
> upon driver induced transmission problems, so network stack has
> a chance to handle the situation.
> 
> Signed-off-by: Oskar Schirmer <oskar@...utronix.de>

You should never have to do this.

As long as netif_carrier_on() and netif_carrier_off() are invoked
properly by the driver, the core networking will never send you
packets when netif_carrier_ok() is false.

I am not applying this patch, drivers should not manage tx queue
state using link status as a condition, that's the job of the
core networking.
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