Date: Tue, 5 Jun 2007 19:12:47 +0200 From: "Attilio Rao" <attilio@freebsd.org> To: "Kostik Belousov" <kostikbel@gmail.com> Cc: 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: <3bbf2fe10706051012h3d322a8fka35b9580b21ce22d@mail.gmail.com> In-Reply-To: <20070605164740.GY2268@deviant.kiev.zoral.com.ua> References: <200706051420.l55EKEih018925@repoman.freebsd.org> <20070606003412.W35544@besplex.bde.org> <20070605150005.GW2268@deviant.kiev.zoral.com.ua> <20070605150521.GX2268@deviant.kiev.zoral.com.ua> <20070606011022.R35623@besplex.bde.org> <3bbf2fe10706050829o2d756a4cu22f98cf11c01f5e4@mail.gmail.com> <3bbf2fe10706050843x5aaafaafy284e339791bcfe42@mail.gmail.com> <20070605164740.GY2268@deviant.kiev.zoral.com.ua>
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2007/6/5, Kostik Belousov <kostikbel@gmail.com>:
> On Tue, Jun 05, 2007 at 05:43:03PM +0200, 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.
>
> With the following patch, I get the
> panic: mutex sched lock recursed at .../kern_synch.c:379
> with backtrace
> mi_switch
> _mtx_unlock_sleep
> _mtx_unlock_flags
> vm_pagezero
>
>
> diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
> index e0592a8..bf44229 100644
> --- a/sys/kern/kern_mutex.c
> +++ b/sys/kern/kern_mutex.c
> @@ -670,7 +670,9 @@ _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
> "_mtx_unlock_sleep: %p switching out lock=%p", m,
> (void *)m->mtx_lock);
>
> + thread_lock(td);
> mi_switch(SW_INVOL, NULL);
> + thread_unlock(td);
> if (LOCK_LOG_TEST(&m->lock_object, opts))
> CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p resuming lock=%p",
> m, (void *)m->mtx_lock);
After I back home I realized there is only sched_lock currently... not
yet per-cpu locks :)
So we should just disable this code for the moment (or forever).
Attilio
--
Peace can only be achieved by understanding - A. Einstein
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