linux-kernel - Re: [PATCH 0/3] resend, cpuset/hotplug fixes

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Date:	Fri, 11 Sep 2009 15:53:24 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham Shenoy <ego@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Jiri Slaby <jirislaby@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Miao Xie <miaox@...fujitsu.com>,
	Paul Menage <menage@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] resend, cpuset/hotplug fixes

Peter Zijlstra wrote:
> On Fri, 2009-09-11 at 15:15 +0800, Lai Jiangshan wrote:
>> One other minor thing:
>> Oleg's patch may introduce a trouble in PREEEMPT_RT tree, because
>> spinlock in RT is also mutex. Likely I'm wrong.
> 
> But they have priority-inheritance, hence you cannot create a deadlock
> through preemption. If the kstopmachine thread blocks on a mutex, the
> owner gets boosted to kstopmachine's prio and runs to completion, after
> that kstopmachine continues.
> 

The deadlock is because the owner is at the dead cpu, It's not because
the owner's prio is low. priority-inheritance can't help it.

I think we need to use a raw spinlock.

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