Re: Kernel 2.4.5-ac2 OOPs when run pppd ?

[Richard Gooch]

Andrew Morton writes:
> Alan Cox wrote:
> > 
> > > Yeas it is stil the same as 2.4.5-ac1, but did not
> > > happen with 2.4.5; You can try running pppd in the
> > > console (tty1) without any argument.
> > 
> > Looks like an interaction with the newer console locking code. The BUG() is
> > caused when the ppp code tries to write to the console from inside an
> > interrupt handler [now not allowed]
> 
> I wondered if there were more cases.
> 
> In the (as-yet-unsent) Linus patch I've added an
> 
> 	if (in_interrupt()) {
> 		shout_loudly();
> 		return;
> 	}
> 
> in three places to catch this possibility.   I'll prepare
> a -ac diff.
> 
> 
> This is a fundamental problem.
> 
> - The console is a tty device
> - tty devices are callable from interrupts
> - the console is very stateful and needs locking
> - the locking must be interrupt-safe (irqsave)
> - the console is very slow.
> 
> net result: we block interrupts for ages.  It's
> an exceptional situation.  I hope Linus buys this
> line of reasoning :)

How about having a helper function for interrupt handlers which queues
characters to be sent to the console? kconsoled anyone? Blocking
interrupts is quite distressing, so we need to be consoled ;-)

				Regards,

					Richard....
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