linux-kernel - Re: [patch] Reorganize the cpufreq cpu hotplug locking to not be totally bizare

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Message-ID: <20060726141531.A22927@unix-os.sc.intel.com>
Date:	Wed, 26 Jul 2006 14:15:31 -0700
From:	Ashok Raj <ashok.raj@...el.com>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Dave Jones <davej@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Chuck Ebbert <76306.1226@...puserve.com>,
	Ashok Raj <ashok.raj@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [patch] Reorganize the cpufreq cpu hotplug locking to not be totally bizare

On Wed, Jul 26, 2006 at 01:22:24PM -0700, Linus Torvalds wrote:
> 
> Of course, that's why people want recursive locks in the first place, and 
> it's also why we've (largely successfully) have avoided them - it allows 
> for people being way too lazy about locking, and allows for really broken 
> schenarios like this.
> 
> I wonder if we could just make the workqueue code just run with preemption 
> disabled - that should also automatically protect against any CPU hotplug 

Its probably ok for this case.

before introducing the ugly recursion we did try the preempt_disable()
for cpufreq, and it worked for most all governers with preempt_disable(), 
but powernowk8 called set_cpus_allowed() in the callback path that 
threw out a scheduling while in atomic BUG().

http://lkml.org/lkml/2005/10/31/239


> events on the local CPU (and I think "local CPU" is all that the wq code 
> cares about, no?)
> 
> 		Linus

-- 
Cheers,
Ashok Raj
- Open Source Technology Center
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