linux-kernel - Re: linux 5.15-rc4: refcount underflow when unloading gpio-mockup

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Date:   Mon, 4 Oct 2021 23:28:44 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: linux 5.15-rc4: refcount underflow when unloading gpio-mockup

On Mon, Oct 04, 2021 at 10:17:54PM +0800, Kent Gibson wrote:
> On Mon, Oct 04, 2021 at 04:20:55PM +0300, Heikki Krogerus wrote:
> > On Mon, Oct 04, 2021 at 08:47:01PM +0800, Kent Gibson wrote:
> > > On Mon, Oct 04, 2021 at 03:30:43PM +0300, Heikki Krogerus wrote:
> > > > On Mon, Oct 04, 2021 at 08:19:42PM +0800, Kent Gibson wrote:
> > > > > On Mon, Oct 04, 2021 at 11:44:17AM +0200, Greg Kroah-Hartman wrote:
> > > > > > On Mon, Oct 04, 2021 at 05:34:16PM +0800, Kent Gibson wrote:
> > > > > > > Hi,
> > > > > > > 

[snip]

> > > Looking at the offending patch, it effectively replaces a call to
> > > device_add_properties() with one to
> > > device_create_managed_software_node(), and those two functions appear
> > > quite different - at least at first glance.
> > > Is that correct?
> > 
> > The only real difference between the two functions is that
> > device_create_managed_software_node() marks the software node it
> > creates (and it does it exactly the same way as
> > device_add_properties()) as "managed" with a specific flag.
> > 
> 

That managed flag makes all the difference.

I've tried to find a fix along the same lines as Laurentiu Tudor's
5aeb05b27f8 software node: balance refcount for managed software nodes
but haven't found anything that works.

What does work for me is to revert the call to
device_create_managed_software_node() to a call to
device_add_properties():

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 652531f67135..2f30bdb94fab 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -826,8 +826,7 @@ struct platform_device *platform_device_register_full(
                goto err;

        if (pdevinfo->properties) {
-               ret = device_create_managed_software_node(&pdev->dev,
-                                                         pdevinfo->properties, NULL);
+               ret = device_add_properties(&pdev->dev, pdevinfo->properties);
                if (ret)
                        goto err;
        }

That obviously wont work with your latest series that removes
device_add_properties(), but that is the simplest, and only, solution
that I've found so far.

Cheers,
Kent.