Date: Tue, 5 Jun 2007 12:30:20 -0400 From: John Baldwin <jhb@freebsd.org> To: "Attilio Rao" <attilio@freebsd.org> Cc: Kostik Belousov <kostikbel@gmail.com>, cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org, Bruce Evans <brde@optusnet.com.au> Subject: Re: cvs commit: src/sys/kern kern_mutex.c Message-ID: <200706051230.21242.jhb@freebsd.org> In-Reply-To: <3bbf2fe10706050843x5aaafaafy284e339791bcfe42@mail.gmail.com> References: <200706051420.l55EKEih018925@repoman.freebsd.org> <3bbf2fe10706050829o2d756a4cu22f98cf11c01f5e4@mail.gmail.com> <3bbf2fe10706050843x5aaafaafy284e339791bcfe42@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tuesday 05 June 2007 11:43:03 am Attilio Rao wrote:
> 2007/6/5, Attilio Rao <attilio@freebsd.org>:
> > 2007/6/5, Bruce Evans <brde@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.
If this is the old #ifndef PREEMPTION manual preemption stuff, then just
remove it. I've been wanting to axe it for a while, rwlocks don't do the
manual preemption either, and if it is getting in the way it's best to just
purge it.
--
John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200706051230.21242.jhb>