linux-kernel - Re: [BUG] cpu-hotplug: Can't offline the CPU with naughty realtime processes

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Message-ID: <20070507110256.GM7311@in.ibm.com>
Date:	Mon, 7 May 2007 16:32:56 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Ashok Raj <ashok.raj@...el.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [BUG] cpu-hotplug: Can't offline the CPU with naughty realtime processes

On Mon, May 07, 2007 at 04:17:24PM +0530, Gautham R Shenoy wrote:
> Nevertheless, with the freezer based approach that we're experimenting,
> this problem shouldn't arise. We expect the whole system to get frozen
> before we actually do a cpu_down() (which will then call
> __stop_machine_run). So any such rogue RT task will have to first fail
> the freezer ( which it will), 

>From what I understand of the freezer, if the RT task is running in user
space (which seems to be the case in this thread), it should get frozen even 
if it is a forever running SCHED_FIFO task at MAX_RT_PRIO -1 priority?

> but that's ok, since on a freezer-fail,
> we just thaw all the processes and get the system up and running again.
> Yeah, the cpu-hotplug operation will fail though.

-- 
Regards,
vatsa
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