Linux-kernel mailing list archive 2000-07,: 2.3.4x softnet watchdog and (isdn) demand dialing

# 2.3.4x softnet watchdog and (isdn) demand dialing

Henner Eisen (eis@baty.hanse.de)
14 Feb 2000 22:31:41 +0100

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Hi,

when porting the isdn driver to use the new softnet tx_timout watchdog
method, we observed a minor problem: We get

NETDEV WATCHDOG: isdn0: transmit timed out

messages in the syslog.

ISDN network interfaces (which tunnel IP traffic on top of ISDN
connections) provide demand-dialing semantics. When the isdn connection
to the peer is down and the network layer submits a packet to the isdn
net_device, the driver will establish the connection automagically
(and might clear the isdn call later when no traffic was on the interface
for a certain amount of time). Of course, when a new IP packet triggers
demand dialing, it sometimes takes some time until the isdn connection
is up. During this time, the isdn net_device is marked as busy (now with
netif_stop_queue()) and is marked up (netif_wake_queue() nowadays) when
the connection is up. That way, existing packets in the packet scheduler's
tx_queue are sent out immediately as soon as the connection is up.

However, if the dialing takes longer than the isdn net_device's timeout,
then each time the watchdog timer is called, the above message is generated.

Maybe some other demand dialing device drivers will suffer from the same
problem.

The messages are harmless, but they certainly will confuse users once
Linux distributions ship with 2.4.x pre-installed. Thus, it would make
sense if we could conditionally suppress the watchdog's warning
messages, increase the timout value, or switch off the watchdog timer
temporarily (while the isdn interface is in the dialing state).

What do you consider the most appropriate or cleanest solution for doing
this?

Henner

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