linux-kernel - Re: [PATCH v3 2/7] xen/pciback: Don't deadlock when unbinding.

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Message-ID: <20140709140106.GE21837@laptop.dumpdata.com>
Date:	Wed, 9 Jul 2014 10:01:06 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	konrad@...nel.org, xen-devel@...ts.xenproject.org,
	boris.ostrovsky@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/7] xen/pciback: Don't deadlock when unbinding.

On Wed, Jul 09, 2014 at 01:21:12PM +0100, David Vrabel wrote:
> On 08/07/14 19:58, konrad@...nel.org wrote:
> > --- a/drivers/xen/xen-pciback/pci_stub.c
> > +++ b/drivers/xen/xen-pciback/pci_stub.c
> > @@ -277,10 +277,15 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
> >  	 * (so it's ready for the next domain)
> >  	 */
> >  
> > -	/* This is OK - we are running from workqueue context
> > -	 * and want to inhibit the user from fiddling with 'reset'
> > +	/* We might be holding the PCI lock (see comment at the top of the
> > +	 * function) - as such try lock and if we can't then don't worry -
> > +	 * as either:
> > +	 *  - we are 'unbind' in which case 'pcistub_device_release' gets
> > +	 *    called which does the locked version of this.
> > +	 *  - the toolstack has the smarts to do it and has done the
> > +	 *    reset on SysFS before assigning this device to another guest.
> >  	 */
> > -	pci_reset_function(dev);
> > +	pci_try_reset_function(dev);
> 
> Why not use __pci_reset_function_locked() and ensure all callers of
> pcistub_put_pci_dev() are holding the device lock?

That could also be done.
> 
> >  	pci_restore_state(dev);
> 
> If we didn't reset the device there is no need to restore its state.

<nods>
> 
> David
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