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Date: Fri, 30 Jan 2009 09:08:35 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Rusty Russell <rusty@rustcorp.com.au>, Mike Travis <travis@sgi.com>,
       Ingo Molnar <mingo@redhat.com>, Dave Jones <davej@redhat.com>,
       cpufreq@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.
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On Fri, 30 Jan 2009 14:49:35 +0100 Ingo Molnar <mingo@elte.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.