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Subject: Re: [PATCH 0/3] resend, cpuset/hotplug fixes
From: Peter Zijlstra <peterz@infradead.org>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
       Gautham Shenoy <ego@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       Jiri Slaby <jirislaby@gmail.com>, Li Zefan <lizf@cn.fujitsu.com>,
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       "Rafael J. Wysocki" <rjw@sisk.pl>,
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Date: Fri, 11 Sep 2009 09:57:52 +0200
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On Fri, 2009-09-11 at 15:53 +0800, Lai Jiangshan wrote:
> 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.

Not in mainline you don't.