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Subject: Re: [PATCH/RFC] timer: fix deadlock on cpu hotplug
From: Peter Zijlstra <peterz@infradead.org>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Tejun Heo <tj@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
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        Arnd Bergmann <arnd@arndb.de>
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Date: Sat, 25 Sep 2010 02:19:47 +0200
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On Thu, 2010-09-23 at 15:31 +0200, Heiko Carstens wrote:
> On Wed, Sep 22, 2010 at 04:29:36PM +0200, Peter Zijlstra wrote:
> > On Wed, 2010-09-22 at 11:22 +0200, Peter Zijlstra wrote:
> > 
> > > The idea was to move it to a class of its own above SCHED_FIFO.
> > > 
> > > I'll try and get something done, but I'm heading out to LinuxCon.JP
> > > soon.
> > 
> > Something like the below, it seems to boot, build a kernel and hotplug.
> 
> Thanks for the fast patch. Yes, it works. Sort of:
> 
> ------------[ cut here ]------------

<SPLAT>

> 
> ..and crashes afterwards ;)

Yeah, I can imagine,. weird though, kthread_create() should leave the
new thread in uninterruptible context. The above warning implies this is
not so.. 

> Btw. I also tried to boot 2.6.35.5 with your patch and it hangs just at
> the beginning. I also had to apply 5e3d20a68f63fc5a310687d81956c3b96e488b84
> "init: Remove the BKL from startup code" to make the machine boot again,
> which was a bit surprising.

Most curious and unexpected,.. I'll try and have a look, but it might
have to wait until after LinuxCon.JP..