linux-kernel - Re: [PATCH v5 09/13] PCI: Introduce /sys/bus/pci/devices/.../remove

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Date:	Tue, 24 Mar 2009 13:32:52 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Alex Chiang <achiang@...com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Oleg Nesterov <oleg@...hat.com>, jbarnes@...tuousgeek.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	kaneshige.kenji@...fujitsu.com,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: [PATCH v5 09/13] PCI: Introduce /sys/bus/pci/devices/.../remove

On Tue, 2009-03-24 at 03:46 -0700, Andrew Morton wrote:

> But I don't think we've seen a coherent description of what's actually
> _wrong_ with the current code.  flush_cpu_workqueue() has been handling
> this case for many years with no problems reported as far as I know.
> 
> So what has caused this sudden flurry of reports?  Did something change in
> lockdep?  What is this
> 
> [  537.380128]  (events){--..}, at: [<ffffffff80257fc0>] flush_workqueue+0x0/0xa0
> [  537.380128]
> [  537.380128] but task is already holding lock:
> [  537.380128]  (events){--..}, at: [<ffffffff80257648>] run_workqueue+0x108/0x230
> 
> supposed to mean?  "events" isn't a lock - it's the name of a kernel
> thread, isn't it?  If this is supposed to be deadlockable then how?

events is indeed the schedule_work workqueue thread name -- I just used
that for lack of a better name.

> Because I don't immediately see what's wrong with e1000_remove() calling
> flush_work().  It's undesirable, and we can perhaps improve it via some
> means, but where is the bug?

There is no bug -- it's a false positive in a way. I've pointed this out
in the original thread, see
http://thread.gmane.org/gmane.linux.kernel/550877/focus=550932

johannes

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