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

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Date:	Tue, 22 May 2012 10:11:41 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <ming.lei@...onical.com>
cc:	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_shutdownā€¸

On Tue, 22 May 2012, Ming Lei wrote:

> On Tue, May 22, 2012 at 2:29 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Mon, 21 May 2012, Ming Lei wrote:
> >> Another candidate fix is to register a reboot notifier in driver core to prevent
> >> driver from being bound or unbound from start of reboot/shutdown, but looks
> >> not easy as the way of holding device locks.
> >
> > I'd guess it was done this way so that the shutdown task wouldn't have
> > to wait for a buggy driver that didn't want to release the device lock
> > (or that crashed while holding the lock).
> 
> Maybe, so I understand you agree on adding the device lock as did
> in the patch, don't I?

I don't know.  It depends on the intention behind the shutdown 
callback.  Maybe each driver is supposed to be responsible for doing 
its own locking.

Do you think that a buggy driver should be able to prevent the system 
from shutting down?

> Also we can add below line before acquiring device lock to help
> toubleshoot buggy driver.
> 
>                dev_dbg(dev, "acquiring device lock for shutdown\n");
> 
> >
> > It's not clear that the reboot notifier approach would work.  What
> > about probes that had already started when notifier was called?
> 
> Looks holding device lock is still needed in the notifier callback for
> handling the case if reboot notifier approach is taken.
> 
> IMO, the way of holding device lock is better than reboot notifier approach.

Yes, it is better.  The question is, is it right?

Alan Stern

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