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

[Lai Jiangshan]

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.