Re: ppp_synctty and in_interrupt

From: Paul Fulghum (
Date: Thu Jun 13 2002 - 10:06:00 EST

> I am currently developing a tty-Driver which is used for synchronous PPP.
> ...
> The ppp_synctty ldisc only calls my ttywrite function in interrupt
> 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

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,
Microgate Corporation,

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