Date: Tue, 23 Nov 2004 23:59:44 -0500 From: Stephan Uphoff <ups@tree.com> To: Mark Gooderum <mark@verniernetworks.com> Cc: freebsd-stable@freebsd.org Subject: Re: propagate_priority KASSERT Message-ID: <1101272384.48967.45.camel@palm.tree.com> In-Reply-To: <41A3FE4E.30007@verniernetworks.com> References: <41A3FE4E.30007@verniernetworks.com>
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On Tue, 2004-11-23 at 22:21, Mark Gooderum wrote:
> We're currently tripping accross the following KASSERT in
> subr_turnstile.c (in 5.3.0 RELEASE):
>
> /*
> * XXX: The owner of a turnstile can be stale if it is the
> * first thread to grab a slock of a sx lock. In that case
> * it is possible for us to be at SSLEEP or some other
> * weird state. We should probably just return if the state
> * isn't SRUN or SLOCK.
> */
> KASSERT(!TD_IS_SLEEPING(td),
> ("sleeping thread %p (pid %d) owns non-sleepable lock %p",
> td, td->td_proc->p_pid, ts))
>
> This is in propagate_priority().
>
> However, propagate_priority() is only called in one place, by
> turnstile_wait(), and turnstile_wait() in turn is only called by
> _mtx_lock_sleep() which in turn is only used for sleep mutexes.
>
> TD_IS_SLEEPING() really means the SLEEPING inhibitor is set which in
> turn seems to mean that thread is in fact on a sleepq - which is used
> for various wait channels and timeouts.
>
> So I'm just trying to understand why it's a 100% assertion for any
> holder of the turnstile for a sleep mutex sleeping.
Priority inheritance is needed to avoid blocking interrupt threads for a
long time. A thread sleeping while holding a mutex would break priority
inheritance. Another reason is that this would add a hidden dependency
to the wakeup thread - this can easily lead to deadlocks.
Can you find out where the owner of the mutex is sleeping?
Stephan
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