Date: Sat, 11 Aug 2007 12:51:58 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: Roman Divacky <rdivacky@freebsd.org> Cc: hackers@freebsd.org Subject: Re: strange KASSERT in _sleep() Message-ID: <20070811195158.GY99491@funkthat.com> In-Reply-To: <20070811124612.GA21695@freebsd.org> References: <20070811124612.GA21695@freebsd.org>
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Roman Divacky wrote this message on Sat, Aug 11, 2007 at 14:46 +0200:
> tsleep() maps to _sleep() with lock = NULL,
>
> the _sleep() contains this:
>
> KASSERT(timo != 0 || mtx_owned(&Giant) || lock != NULL ||
> ident == &lbolt, ("sleeping without a lock"));
>
>
> which simplifies for tsleep(foo, ...) where foo != lbolt to
> "timo != 0 || mtx_owned(&Giant)"
>
> why do I have to hold Giant or have timo != 0 when calling tsleep?
To prevent a deadlock.. It would be possible for you to miss your
wakeup if you don't have a lock (such as Giant) held... By forcing
a timeout, you guarantee that it will check the condition sometime
in the future...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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