linux-kernel - Re: Race condition between driver_probe_device and device

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Message-ID: <Pine.LNX.4.44L0.1212071023090.1565-100000@iolanthe.rowland.org>
Date:	Fri, 7 Dec 2012 10:25:59 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <ming.lei@...onical.com>
cc:	Wedson Almeida Filho <wedsonaf@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	Linux PM List <linux-pm@...r.kernel.org>
Subject: Re: Race condition between driver_probe_device and device_shutdown

On Fri, 7 Dec 2012, Ming Lei wrote:

> > I guess the question is whether the callee is allowed to call
> > device_move(), if not, we're good.
> 
> Not only the callee, and other contexts can change device->parent
> too. Looks rfcomm_tty_open() which calls device_move() is called
> in open() context, so the parent might be changed before unlock(dev->parent)
> in __driver_attach().
> 
> >
> >> Your concern on device_remove() might be correct. Also, I am wondering
> >> if we can walk the 'dpm_list' backwards for device shutdown, which should
> >> be simpler and more reasonable.
> >
> > How would that help?
> 
> device_pm_lock() can prevent device_move() from being running.

That wouldn't prevent problems during unbinding.  Wedson is right; the 
places that lock dev->parent must save a local copy of dev->parent.

Alan Stern

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