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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jiang Liu <jiang.liu@linux.intel.com>, mingo@kernel.org,
        "Rafael J. Wysocki" <rafael@kernel.org>, Tejun Heo <tj@kernel.org>,
        linux hotplug mailing <linux-hotplug@vger.kernel.org>,
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        ACPI Devel Maling List <linux-acpi@vger.kernel.org>
Subject: Re: Possible deadlock related to CPU hotplug and kernfs
Date: Wed, 09 Sep 2015 00:28:12 +0200
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On Tuesday, September 08, 2015 12:40:08 PM Peter Zijlstra wrote:
> On Mon, Sep 07, 2015 at 11:33:21PM +0200, Rafael J. Wysocki wrote:
> > On Monday, September 07, 2015 11:11:19 AM Jiang Liu wrote:
> > Peter, Ingo, some help from lockdep expert is needed.
> > 
> > We have a splat that almost certainly is a false positive (the original report
> > is here http://marc.info/?l=linux-kernel&m=144109156901959&w=4) and no ideas
> > how to make it go away.  Can you please have a look and advise?
> 
> I can't even find the relevant code :/
> 
> From that email I get kernfs_fop_write() which calls
> kernfs_get_active(), but that does _NOT_ call cpu_up(), so that
> callchain is shite.
> 
> The actual lockdep splat is also not really helpful, and is spraying
> names over: acpi, device, sysfs and kernfs (do we really need that many
> layeres of obfuscation for a simple file?)
> 
> So, please, start by explaining the thing proper such that simple people
> like me know what to look for.

OK, I'll try to get that later this week.

Or maybe Jiang Liu can beat me to doing that. :-)

Thanks,
Rafael