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

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Date:	Tue, 24 Mar 2009 14:21:13 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Alex Chiang <achiang@...com>,
	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 12:17 +0100, Peter Zijlstra 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.
> 
> Might be sheer luck, but afaik we did have some actual deadlocks due to
> workqueue flushing -- a particular one I can remember was cpu-hotplug vs
> cpufreq.

Two cases are relevant here actually -- the recursion which hasn't ever
shown up before, and a number of possible deadlocks of e.g. some people
doing, effectively:

	rtnl_lock();
	flush_scheduled_work();
	rtnl_unlock();

vs. the linkwatch work that can, at this point in time, still be queued,
and needs the rtnl as well.

A little digging through git logs finds more references, e.g. commits
f90d4118bacef87894621a3e8aba853fa0c89abc and
fd781fa25c9e9c6fd1599df060b05e7c4ad724e5.

Some others were fixed that I remember, but apparently without putting
the lockdep report into the commit log.

johannes

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