Re: Kernel 2.4.5-ac2 OOPs when run pppd ?

[Andrew Morton]

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 :)

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