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

From: Daniel Lang (dl_at_leo.org)
Date: 06/30/04

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    Date: Wed, 30 Jun 2004 10:05:15 +0200
To: Colin Percival <colin.percival@wadham.ox.ac.uk>

    Hi,

    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,
     Daniel 

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