linux-kernel - Re: sysfs: cannot create duplicate filename

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Message-ID: <20110412160220.GA28483@suse.de>
Date:	Tue, 12 Apr 2011 09:02:20 -0700
From:	Greg KH <gregkh@...e.de>
To:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: sysfs: cannot create duplicate filename

On Tue, Apr 12, 2011 at 04:39:49PM +0200, Sebastian Ott wrote:
> 
> 
> On Mon, 11 Apr 2011, Greg KH wrote:
> 
> > On Mon, Apr 11, 2011 at 07:50:34PM +0200, Sebastian Ott wrote:
> > > 
> > > 
> > > On Mon, 11 Apr 2011, Greg KH wrote:
> > > 
> > > > On Mon, Apr 11, 2011 at 05:05:08PM +0200, Sebastian Ott wrote:
> > > > > 
> > > > > 
> > > > > On Mon, 11 Apr 2011, Greg KH wrote:
> > > > > 
> > > > > > On Mon, Apr 11, 2011 at 04:33:03PM +0200, Sebastian Ott wrote:
> > > > > > > On Mon, 11 Apr 2011, Greg KH wrote:
> > > > > > > 
> > > > > > > > On Mon, Apr 11, 2011 at 04:04:08PM +0200, Sebastian Ott wrote:
> > > > > > > > > Hi,
> > > > > > > > > 
> > > > > > > > > i've seen this warning which looks to be caused by a race between device_add
> > > > > > > > > and driver_register
> > > > > > > > > 
> > > > > > > > > [   80.893594] sysfs: cannot create duplicate filename '/bus/ccw/drivers/qeth/0.0.b57d'
> > > > > > > > 
> > > > > > > > Isn't the problem here the fact that you are creating 2 directories of
> > > > > > > > the same name?
> > > > > > > I'm sure this isn't the case here. The bus code just calls device_add and
> > > > > > > at the same time on a different thread a module is loaded which registers
> > > > > > > a driver at the bus.
> > > > > > > 
> > > > > > > I was able to reproduce this with a module which creates a dummy bus
> > > > > > > and registers drivers and devices on this bus on 2 different workqueues.
> > > > > > 
> > > > > > That makes sense, as no bus should be doing this on multiple "threads".
> > > > > > What real-life bus does this today?
> > > > > A bus that will recognize and register a lot of devices, after the first
> > > > > uevent is presented to userspace, a module will be loaded registering a
> > > > > driver from a different thread. I don't think thats uncommon.
> > > > 
> > > > But again, what kernel code today does this?  I think they all have
> > > > locks to keep this from happening, right?
> > > I couldn't find a bus who protects device_register against driver_register
> > > and I don't think this is something which should be handled by every
> > > individual bus but from within the driver core.
> > 
> > How did you cause the oops in this original message?  What type of bus
> > was it on?  And did your patch solve the issue?
> 
> I've seen this warning on a system which had a lot of devices attached.
> Those devices also responded _very_ slow. So it took some time to
> register all these deivces (qeth) on the bus (ccw). During this time
> the qeth module got loaded and registered the qeth driver.
> 
> Since i've never seen this warning and those devices normally don't
> take so much time to respond I wrote the beforementioned module to
> reproduce the race and make sure that this is no driver issue.
> 
> With this module the warning could be triggered after a few cycles.
> With the patch applied, I did not see the warning again even after
> > 10.000 cycles.

Ok, fair enough.  Care to resend the patch again so I can review it once
more?

thanks,

greg k-h
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