Date: Mon, 4 Oct 2004 21:14:10 +0200 From: Peter Holm <peter@holm.cc> To: Julian Elischer <julian@elischer.org> Cc: Stephan Uphoff <ups@tree.com> Subject: Re: scheduler (sched_4bsd) questions Message-ID: <20041004191410.GA8423@peter.osted.lan> In-Reply-To: <41619D29.1000704@elischer.org> References: <1095468747.31297.241.camel@palm.tree.com> <1096496057.3733.2163.camel@palm.tree.com> <1096603981.21577.195.camel@palm.tree.com> <200410041131.35387.jhb@FreeBSD.org> <1096911278.44307.17.camel@palm.tree.com> <20041004184939.GA8178@peter.osted.lan> <41619D29.1000704@elischer.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, Oct 04, 2004 at 11:57:45AM -0700, Julian Elischer wrote:
> can you run ktrdump against teh corefile and get the ktr output?
> (you do have it enabled right?)
>
No, that's one of the problems: doadump() fails with this specific panic.
- Peter
>
> Peter Holm wrote:
>
> >On Mon, Oct 04, 2004 at 01:34:38PM -0400, Stephan Uphoff wrote:
> >
> >
> >>On Mon, 2004-10-04 at 11:31, John Baldwin wrote:
> >>
> >>
> >>>On Friday 01 October 2004 12:13 am, Stephan Uphoff wrote:
> >>>
> >>>
> >>>>On Wed, 2004-09-29 at 18:14, Stephan Uphoff wrote:
> >>>>
> >>>>
> >>>>>I was looking at the MUTEX_WAKE_ALL undefined case when I used the
> >>>>>critical section for turnstile_claim().
> >>>>>However there are bigger problems with MUTEX_WAKE_ALL undefined
> >>>>>so you are right - the critical section for turnstile_claim is pretty
> >>>>>useless.
> >>>>>
> >>>>>
> >>>>Arghhh !!!
> >>>>
> >>>>MUTEX_WAKE_ALL is NOT an option in GENERIC.
> >>>>I recall verifying that it is defined twice. Guess I must have looked at
> >>>>the wrong source tree :-(
> >>>>This means yes - we have bigger problems!
> >>>>
> >>>>Example:
> >>>>
> >>>>Thread A holds a mutex x contested by Thread B and C and has priority
> >>>>pri(A).
> >>>>
> >>>>Thread C holds a mutex y and pri(B) < pri(C)
> >>>>
> >>>>Thread A releases the lock wakes thread B but lets C on the turnstile
> >>>>wait queue.
> >>>>
> >>>>An interrupt thread I tries to lock mutex y owned by C.
> >>>>
> >>>>However priority inheritance does not work since B needs to run first to
> >>>>take ownership of the lock.
> >>>>
> >>>>I is blocked :-(
> >>>>
> >>>>
> >>>Ermm, if the interrupt happens after x is released then I's priority
> >>>should propagate from I to C to B.
> >>>
> >>>
> >>There is a hole after the mutex x is released by A - but before B can
> >>claim the mutex. The turnstile for mutex x is unowned and interrupt
> >>thread I when trying to donate its priority will run into:
> >>
> >> if (td == NULL) {
> >> /*
> >> * This really isn't quite right. Really
> >> * ought to bump priority of thread that
> >> * next acquires the lock.
> >> */
> >> return;
> >> }
> >>
> >>So B needs to run and acquire the mutex before priority inheritance
> >>works again and does not get a priority boost to do so.
> >>
> >>This is easy to fix and MUTEX_WAKE_ALL can be removed again at that time
> >>- but my time budget is limited and Peter has an interesting bug left
> >>that has priority.
> >>
> >>
> >
> >I'm not closer to being able to create this panic in a controlled way.
> >After a whole day of different tests I finally got this panic:
> >http://www.holm.cc/stress/log/cons81.html. The trigger seems to be one
> >particular Java applet, but it is not easily reproduceable.
> >
> >- Peter
> >
> >
> >
> >>>If the interrupt happens before x is released,
> >>>then the final bit of propagate_priority() should handle it since it
> >>>resorts the turnstile's thread queue so that C will be awakened rather
> >>>than B.
> >>>
> >>>
> >>Agreed.
> >>
> >> Stephan
> >>
> >>
> >_______________________________________________
> >freebsd-arch@freebsd.org mailing list
> >http://lists.freebsd.org/mailman/listinfo/freebsd-arch
> >To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org"
> >
> >
--
Peter Holm
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20041004191410.GA8423>