From: Scott Wood <scott@timesys.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: john cooper <john.cooper@timesys.com>,
Mark_H_Johnson@raytheon.com,
Karsten Wiese <annabellesgarden@yahoo.de>,
Bill Huey <bhuey@lnxw.com>, Adam Heath <doogie@debian.org>,
"K.R. Foley" <kr@cybsft.com>,
linux-kernel@vger.kernel.org,
Florian Schmidt <mista.tapas@gmx.net>,
Fernando Pablo Lopez-Lezcano <nando@ccrma.Stanford.EDU>,
Lee Revell <rlrevell@joe-job.com>,
Rui Nuno Capela <rncbc@rncbc.org>,
Thomas Gleixner <tglx@linutronix.de>,
Michal Schmidt <xschmi00@stud.feec.vutbr.cz>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1
Date: Fri, 5 Nov 2004 16:42:38 -0500 [thread overview]
Message-ID: <20041105214238.GA11075@yoda.timesys> (raw)
In-Reply-To: <20041104194416.GC10107@elte.hu>
On Thu, Nov 04, 2004 at 08:44:16PM +0100, Ingo Molnar wrote:
>
> * john cooper <john.cooper@timesys.com> wrote:
> >
> > This is a fairly gnarly problem to address. The obvious solution is
> > to hold spinlocks in the mutexes as the dependency tree is atomically
> > traversed. However this will deadlock under MP due to the
> > unpredictable order of mutexes traversed. If the dependency chain is
> > not traversed (and semantics applied) atomically, races exist which
> > cause promotion decisions to be made on [now] stale data.
>
> is the order of locks in the dependency chain really unpredictable? If
> two chain walkers get two locks in opposite order, doesnt that mean that
> the lock ordering (as attempted by the blocked tasks) is deadlock-prone
> already? I.e. this scenario should not happen.
It *shouldn't*, but bugs do happen, and it'd be nice if a mutex
deadlock didn't get promoted into a less debuggable spinlock
deadlock. Plus, if there's any intention of ever exporting this
priority inheritance mechanism to userspace locks, we don't want to
promote a userspace deadlock into a kernel one.
Given how rarely contention should occur, I don't think that a single
lock would be a bottleneck except for obscenely large SMP machines.
-Scott
next prev parent reply other threads:[~2004-11-05 21:42 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-04 16:22 [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1 Mark_H_Johnson
2004-11-04 16:30 ` Ingo Molnar
2004-11-04 16:32 ` Ingo Molnar
2004-11-04 18:59 ` john cooper
2004-11-04 19:44 ` Ingo Molnar
2004-11-04 23:25 ` john cooper
2004-11-05 21:42 ` Scott Wood [this message]
2004-11-05 22:36 ` Bill Huey
2004-11-08 14:35 ` Esben Nielsen
2004-11-08 15:42 ` Ingo Molnar
2004-11-08 22:47 ` Bill Huey
2004-11-06 7:42 ` Ingo Molnar
-- strict thread matches above, loose matches on Subject: below --
2004-11-04 19:39 Mark_H_Johnson
2004-11-04 19:52 ` Ingo Molnar
2004-11-04 17:52 Mark_H_Johnson
2004-11-04 16:53 Mark_H_Johnson
2004-11-04 16:04 Mark_H_Johnson
2004-11-04 16:13 ` Ingo Molnar
2004-11-04 16:17 ` Ingo Molnar
2004-11-04 15:02 Mark_H_Johnson
2004-11-04 15:16 ` Ingo Molnar
2004-11-04 15:19 ` Ingo Molnar
2004-11-03 20:40 Mark_H_Johnson
2004-11-03 18:24 Mark_H_Johnson
2004-10-18 14:50 [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U5 Ingo Molnar
2004-10-19 12:46 ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U6 Ingo Molnar
2004-10-19 18:00 ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U7 Ingo Molnar
2004-10-20 9:45 ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8 Ingo Molnar
2004-10-21 13:27 ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U9 Ingo Molnar
2004-10-22 13:35 ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U9.3 Ingo Molnar
2004-10-22 15:50 ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-U10 Ingo Molnar
2004-10-22 17:56 ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-U10.2 Ingo Molnar
2004-10-25 10:40 ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0 Ingo Molnar
2004-10-27 0:15 ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.3 Ingo Molnar
2004-11-03 10:58 ` [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1 Ingo Molnar
2004-11-03 13:44 ` Lorenzo Allegrucci
2004-11-03 13:46 ` Ingo Molnar
2004-11-03 17:53 ` Lorenzo Allegrucci
2004-11-03 20:41 ` Lorenzo Allegrucci
2004-11-03 20:43 ` Ingo Molnar
2004-11-03 21:05 ` Lorenzo Allegrucci
2004-11-03 19:33 ` john cooper
2004-11-03 23:03 ` Magnus Naeslund(t)
2004-11-04 6:56 ` Ingo Molnar
2004-11-04 19:34 ` Gunther Persoons
2004-11-04 20:31 ` Chris Friesen
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