cvs commit: src/sys/kern kern_mutex.c

[Attilio Rao]

2007/6/5, Attilio Rao <attilio at freebsd.org>:
> 2007/6/5, Bruce Evans <brde at optusnet.com.au>:
> >
> > I get a "spin lock held too long" panic during (an interrupt in?) acpi
> > initialization on booting non-PREEMPTION SCHED_4BSD SMP.  Haven't tried
> > other cases.
>
> Do you have a backtrace or any other debugging stuffs available?

Mmm, I think I got the bug.
basically, in kern_mutex.c::_mtx_unlock_sleep(), in the not-preemptive
case what happens at some point is:

td = curthread;
if (td->td_critnest > 0 || td1->td_priority >= td->td_priority)
         return;

thread_lock(td1);
if (!TD_IS_RUNNING(td1)) {
...

mi_switch(SW_INVOL, NULL);
...
}
thread_unlock(td1);

Which is wrong beacause td1 is not curthread and really curthread
should be locked too when context switching.

To a first look the idea is that td and td1 should be locked both, but
I just want more time to look better at it.

Attilio


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