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

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Date:	Wed, 26 Jul 2006 13:22:24 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
cc:	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, 26 Jul 2006, Arjan van de Ven wrote:
> 
> As a quick hack I made non-lock_cpu_hotplug()'ing versions of the 3 key
> workqueue functions (patch below). It works, it's correct, it's just so
> ugly that I'm almost too ashamed to post it. I haven't found a better
> solution yet though... time to take a step back I suppose.

That really is _way_ too ugly for words.

For 2.6.18, we may just have to leave the recursive locking in place, and 
just remove the warning. With the recursive lock, if/when somebody needs 
to take that lock early, the code can just do so, and then the inner 
lock-taker ends up being a no-op.

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

		Linus
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