sio vs sched_lock LOR (was: Re: kern/68442: panic - acquiring duplicate lock of same type: "sleepq chain")

Daniel Lang dl at
Wed Jun 30 01:05:49 PDT 2004


Colin Percival wrote on Tue, Jun 29, 2004 at 10:58:29PM -0700:
> Regardless of the questionable validity of the other problems this machine
> is encountering, this LOR is real (and ugly).  calcru() asserts that it is
> holding sched_lock, but it can printf() about negative runtime or runtime
> going backwards.  With a serial console attached, these messages end up at
> siocnputc(), which needs sio_lock.

Yes, I get lots of 'calcru' messages on the console.

> Now, I presume that there is some reason why the locking order hard-coded
> into witness makes it illegal to pick up sio_lock while holding sched_lock,
> but I can't see it.  Maybe someone else can explain?
> In the mean time, a workaround for this LOR is to unplug the serial console. :-)

ARGL :-)

Well, if this keeps the machine from locking up, I'll try it...

Best regards,
IRCnet: Mr-Spock  
   - In dieser Mail ist ein Geist, der Dich in den Hintern beisst - 
 Daniel Lang * dl at * +49 89 289 18532 *
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