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

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Message-ID: <20120524021429.GB12557@kroah.com>
Date:	Wed, 23 May 2012 19:14:29 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Wedson Almeida Filho <wedsonaf@...il.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 Thu, May 24, 2012 at 09:39:46AM +0800, Ming Lei wrote:
> On Wed, May 23, 2012 at 11:06 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Wed, 23 May 2012, Ming Lei wrote:
> >> The .shutdown callback pointer is got from device->driver, which is
> >> changed in probe and release path. Also runtime PM thing has been
> >> involved into shutting down recently, so looks not only hardware parts
> >> are involved now.
> >
> > This is a tricky question.  Overall I think you're probably right.
> >
> > It's certainly true that holding the device lock across the shutdown
> > callback is the easiest and most reliable way to prevent these races.
> 
> But holding device lock across .shutdown is very inefficient because
> most of devices' driver have not shutdown callback, so I think it is better
> to fix the race by prevent driver core from probing or releasing once
> shutdown is started.
> 
> How about the below patch?

How about waiting for the original poster to respond as to exactly how
they are hitting this race before doing anything?

greg k-h
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