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

From: Ashok Raj
Date: Wed Jul 26 2006 - 17:39:15 EST

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().

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

Ashok Raj
- Open Source Technology Center
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