linux-kernel - Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put

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Message-ID: <52CA8CD1.6080003@citrix.com>
Date:	Mon, 6 Jan 2014 11:00:33 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Levente Kurusa <levex@...ux.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put_device
 call

On 06/01/14 10:00, Ian Campbell wrote:
> On Thu, 2014-01-02 at 13:53 +0000, David Vrabel wrote:
>> On 19/12/13 15:03, Levente Kurusa wrote:
>>> This is required so that we give up the last reference to the device.
>>>
>>> Signed-off-by: Levente Kurusa <levex@...ux.com>
>>> ---
>>>  drivers/xen/xenbus/xenbus_probe.c | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
>>> index 3c0a74b..4abb9ee 100644
>>> --- a/drivers/xen/xenbus/xenbus_probe.c
>>> +++ b/drivers/xen/xenbus/xenbus_probe.c
>>> @@ -465,8 +465,10 @@ int xenbus_probe_node(struct xen_bus_type *bus,
>>>  
>>>  	/* Register with generic device framework. */
>>>  	err = device_register(&xendev->dev);
>>> -	if (err)
>>> +	if (err) {
>>> +		put_device(&xendev->dev);
>>>  		goto fail;
>>> +	}
>>>  
>>>  	return 0;
>>>  fail:
>>
>> There is a kfree(xendev) here so this introduces a double-free.
> 
> How? put_device doesn't touch xendev itself, does it? It just drops the
> ref on the dev member which is not separately dynamically allocated and
> so not freed either.

Releasing all references to the struct device frees the containing
structure via xenbus->dev.release. i.e., xenbus_dev_release() which does
kfree(xendev).

David
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