linux-kernel - Re: [PATCH 1/1] uio: Fix uio

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Date:   Tue, 13 Jun 2017 19:16:14 -0500
From:   Mike Christie <mchristi@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     manish.rangankar@...ium.com, target-devel@...r.kernel.org,
        nab@...ux-iscsi.org, kys@...rosoft.com, haiyangz@...rosoft.com,
        sthemmin@...rosoft.com, mst@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] uio: Fix uio_device memory leak

On 06/13/2017 09:01 AM, Greg KH wrote:
> On Wed, Jun 07, 2017 at 03:06:44PM -0500, Mike Christie wrote:
>> It looks like there might be 2 issues with the uio_device allocation, or it
>> looks like we are leaking the device for possibly a specific type of device
>> case that I could not find but one of you may know about.
>>
>> Issues:
>> 1. We use devm_kzalloc to allocate the uio_device, but the release
>> function, devm_kmalloc_release, is just a noop, so the memory is never freed.
> 
> What do you mean by this?  If the release function is a noop, lots of
> memory in the kernel is leaking.  UIO shouldn't have to do anything
> special here, is the devm api somehow broken?

Sorry. I misdiagnosed the problem. It's a noop, but we did kfree on the
entire devres and its data later.

The problem I was hitting is that memory is not freed until the parent
is removed. __uio_register_device does:

        idev = devm_kzalloc(parent, sizeof(*idev), GFP_KERNEL);
        if (!idev) {
                return -ENOMEM;
        }

so the devres's memory is associated with the parent. Is that intentional?