linux-kernel - Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

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Date:	Fri, 30 Jan 2009 09:08:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>, Ingo Molnar <mingo@...hat.com>,
	Dave Jones <davej@...hat.com>, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

On Fri, 30 Jan 2009 14:49:35 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> > So we still don't have any non-buggy proposal.
> 
> Current upstream code is not pretty (due to the extra workqueue) but not 
> buggy either. You'd be right to point out that it is easy to insert a bug 
> into it and thus it's not pleasant (more of a workaround than a real fix) 
> but if it's outright buggy then please talk up.

OK, so we're not aware of anything in there which will trigger the bug
yet.  Although allocate_threshold_blocks() takes about half the locks in
the kernel - it can run an ext3 commit, it does netlink tx, synchronous
process exec, etc.

Why not give up and kill the whole work_on_cpu() thing?  afaict the
only caller which cannot be immediately switched to use an IPI is
mce_amd_64's allocate_threshold_blocks(), and it looks like that can be
trivially fixed by moving the entire function except for one rdmsr() up
into the caller.  

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