linux-kernel - Re: [PATCH 0/4] treewide: add missing put

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Message-ID: <52AD606F.50408@linux.com>
Date:	Sun, 15 Dec 2013 08:55:27 +0100
From:	Levente Kurusa <levex@...ux.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] treewide: add missing put_device calls

On 12/14/2013 06:24 PM, Greg Kroah-Hartman wrote:
> On Fri, Dec 13, 2013 at 01:42:05PM -0700, Bjorn Helgaas wrote:
>> [+cc Greg]
>>
>> On Fri, Dec 13, 2013 at 12:22 PM, Levente Kurusa <levex@...ux.com> wrote:
>>> Hi,
>>>
>>> This is just the beginning of patchset-set that aims to fix possible
>>> problems caused by not calling put_device() if device_register() fails.
>>>
>>> The root cause for the need to call put_device() is that the underlying
>>> kobject still has a reference count of 1. Thus, device.release() will not
>>> be called and the device will just sit there waiting for a put_device().
>>> Adding the put_device() also removes the need for the call to kfree() as most
>>> release functions already call kfree() on the container of the device.
>>>
>>> While these have not been experienced, they are potential issues and thus
>>> they need to be fixed. Also, they are a few more files that have the same
>>> kind of issue, those will be fixed if these are accepted.
>>
>> Thanks for doing this.  This is the sort of mistake that just gets
>> copied everywhere, so fixing the examples in the tree will help
>> prevent the problem from spreading more.
>>
>> I don't know if there's really value in having device_register()
>> return an error but rely on the caller to do the put_device().  Are
>> there cases where the caller still needs the struct device even if
>> device_register() fails?  E.g., could we do something like this
>> instead (I know some callers would also require corresponding changes
>> to avoid double puts):

There are cases where it is needed. There are quite a few files which
when device_register() fails, the driver print an error messages. IIRC,
there are also a few where the device is also unregistered from the
specific subsystem's core.

-- 
Regards,
Levente Kurusa
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