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

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Message-ID: <53BD33B8.9020901@citrix.com>
Date:	Wed, 9 Jul 2014 13:21:12 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	<konrad@...nel.org>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>, <linux-kernel@...r.kernel.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v3 2/7] xen/pciback: Don't deadlock when unbinding.

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?

>  	pci_restore_state(dev);

If we didn't reset the device there is no need to restore its state.

David
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