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Date:	Mon, 28 Jul 2014 14:06:59 +0100
From:	David Vrabel <>
To:	Konrad Rzeszutek Wilk <>,
	<>, <>,
	<>, <>
CC:	<>
Subject: Re: [PATCH v5 2/6] xen/pciback: Don't deadlock when unbinding.

On 14/07/14 17:18, Konrad Rzeszutek Wilk wrote:
> As commit 0a9fd0152929db372ff61b0d6c280fdd34ae8bdb
> 'xen/pciback: Document the entry points for 'pcistub_put_pci_dev''
> explained there are four entry points in this function.
> Two of them are when the user fiddles in the SysFS to
> unbind a device which might be in use by a guest or not.
> Both 'unbind' states will cause a deadlock as the the PCI lock has
> already been taken, which then pci_device_reset tries to take.
> We can simplify this by requiring that all callers of
> pcistub_put_pci_dev MUST hold the device lock. And then
> we can just call the lockless version of pci_device_reset.
> To make it even simpler we will modify xen_pcibk_release_pci_dev
> to quality whether it should take a lock or not - as it ends
> up calling xen_pcibk_release_pci_dev and needs to hold the lock.
> CC:

This deadlock is for a rather specific and uncommon use case (manually
unbinding a PCI while it is passed-through). Is this critical enough to
warrant a stable backport?

> Reviewed-by: Boris Ostrovsky <>
> Signed-off-by: Konrad Rzeszutek Wilk <>

Reviewed-by: David Vrabel <>

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