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From: "Paul Fulghum" <paulkf@microgate.com>
To: <klaus.herb@ikon-gmbh.de>, <linux-kernel@vger.kernel.org>
In-Reply-To: <01C212F6.F1993680.klaus.herb@ikon-gmbh.de>
Subject: Re: ppp_synctty and in_interrupt
Date: Thu, 13 Jun 2002 10:06:00 -0500
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> 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

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