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

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Date:	Wed, 23 May 2012 11:06:27 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <ming.lei@...onical.com>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	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 Wed, 23 May 2012, Ming Lei wrote:

> >> Do you think that a buggy driver should be able to prevent the system
> >> from shutting down?
> 
> IMO, the buggy driver should be fixed first, not only in .probe or .release, but
> also in .runtime_resume, all may affect shutting down.
> 
> >
> > The original intent of the shutdown callback was to just the hardware
> > part of the device shutdown and not do muck with kernel data structures
> > because just the device portion should be more reliable and was all
> > that is needed.
> 
> 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.

Alan Stern

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