From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@9fans.net
From: erik quanstrom <quanstro@coraid.com>
Date: Fri, 29 Aug 2008 14:26:48 -0400
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Subject: Re: [9fans] notes and traps
Topicbox-Message-UUID: 0aa956e6-ead4-11e9-9d60-3106f5b1d025

> i can reproduce it with this:
>
> http://cm.bell-labs.com/sources/contrib/cinap_lenrek/traptest/
>
> 8c test.c
> 8a int80.s
> 8l test.8 int80.8
> ./8.out
>
> 8.out 12490667: suicide: sys: trap: general protection violation
> pc=0x00001333

okay.  it seems pretty clear from the code that you're dead meat
if you receive a note while you're in the note handler.  that is,
up->notified = 1.  it looks pretty clear that this is intentional.
i don't see why one couldn't get 3-4 note before the note handler
is called, however.

given this, calling sleep() from the note handler is an especially
bad idea.

however, on a multiprocessor (or if you get scheduled by a clock
tick on a up), you're still vulnerable.  this is akin to hitting ^c
twice quickly — and watching one's shell exit.

it would be good to track down what's really going on in your
vm.  how many processors does plan 9 think it has?

i did some looking to see if i could find any discussions on the
implementation of notes and didn't find anything in my quick scan.
it would be very interesting to have a little perspective from someone
who was there.

- erik