ppp_synctty and in_interrupt

ppp_synctty and in_interrupt

[Klaus Herb]

Hello,
I am currently developing a tty-Driver which is used for synchronous PPP.

System:
Board		Special Hardware with a Motorola XPC8260 Microcontroller
OS		Elinos V2 with Kernel Version 2.4.3
PPP		pppd and ppp Modules Version 2.4.1

The following Problem occurs:

The ppp_synctty ldisc only calls my ttywrite function in interrupt context. 
But to avoid a race condition I must include a Semaphore in my ttywrite 
function, so I get a Kernel Oops when this Semaphore causes a call to 
schedule().

Is there a way to stop this ppp_synctty ldisc from sending in Interrupt 
Context?
or
Why does this ldisc only write in interrupt context?


Please CC your replay to klaus.herb@ikon-gmbh.de


Thanks!

Klaus Herb

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Klaus Herb
ikon GmbH
Benzstrasse 17
89079 Ulm
Germany

phone  +49/731/94661-0
fax       +49/731/94661-61
mailto:klaus.herb@ikon-gmbh.de
http://www.ikon-gmbh.de
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Re: ppp_synctty and in_interrupt

[Paul Fulghum]

> I am currently developing a tty-Driver which is used for synchronous PPP.
> ...
> The ppp_synctty ldisc only calls my ttywrite function in interrupt
context.
> But to avoid a race condition I must include a Semaphore in my ttywrite
> function, so I get a Kernel Oops when this Semaphore causes a call to
> schedule().
>
> Is there a way to stop this ppp_synctty ldisc from sending in Interrupt
> Context?
> or
> Why does this ldisc only write in interrupt context?
>
> Please CC your replay to klaus.herb@ikon-gmbh.de

It should not call the tty write function in interrupt context.

The ldisc will call the tty write in two situtations:
1. when a new packet to send is available
2. when the tty driver calls the ldisc write_wakeup
  to send queued frames

My guess is that your driver is calling write_wakeup
in an interrupt context (in response to a tx complete IRQ).
You should call write_wakeup() from a bottom half
handler scheduled by the interrupt service routine instead
of directly from the ISR.

Paul Fulghum, paulkf@microgate.com
Microgate Corporation, www.microgate.com