Messages in this thread | | | Date | Mon, 16 Dec 2013 18:18:53 +0100 | From | Levente Kurusa <> | Subject | Re: [PATCH 0/4] treewide: add missing put_device calls |
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On 12/15/2013 06:03 PM, Greg Kroah-Hartman wrote: > On Sun, Dec 15, 2013 at 08:55:27AM +0100, Levente Kurusa wrote: >> 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@linux.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. > > That shouldn't be needed, and can be removed. Yes, we could put a pr_warn() when device_register() fails.
> >> IIRC, there are also a few where the device is also unregistered from >> the specific subsystem's core. > > Do you have a specific example of this? This should happen in the > release function of the device already, not in some other code. > Character drivers who register with device_register() call cdev_del() when device_register() fails. cdev_del() in turn calls kobject_put on the kobject of the device. Of course, this could also be replaced. Anyways, I have another set of these patches (approx 40) that I will post in a day or so. With that most (if not all) should be fixed.
-- Regards, Levente Kurusa
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