linux-kernel - Re: v5.13-rcX regression - NULL pointer dereference

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Message-ID: <YNH1bo6BesNGY3gu@owl.dominikbrodowski.net>
Date:   Tue, 22 Jun 2021 16:36:30 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: v5.13-rcX regression - NULL pointer dereference - MFD and
 software node API

Am Tue, Jun 22, 2021 at 05:10:44PM +0300 schrieb Heikki Krogerus:
> On Tue, Jun 22, 2021 at 11:09:58AM +0300, Heikki Krogerus wrote:
> > On Mon, Jun 21, 2021 at 05:31:50PM +0200, Dominik Brodowski wrote:
> > > Am Mon, Jun 21, 2021 at 01:37:59PM +0300 schrieb Heikki Krogerus:
> > > > On Mon, Jun 21, 2021 at 01:00:06PM +0300, Andy Shevchenko wrote:
> > > > > Can you, please, attach this to the bug report?
> > > > > 
> > > > > Long story here is that the device creation fails but we already have added
> > > > > swnode to it. Meanwhile, device itself is not completely instantiated (yet)
> > > > > and dev_name(dev) is NULL. The software_node_notify() is called with such
> > > > > device and Oopses in the following line
> > > > > 
> > > > > 	sysfs_remove_link(&swnode->kobj, dev_name(dev));
> > > > > 
> > > > > My patch fixes another issue that might happen before this and in the code
> > > > > that retrieves swnode itself in the device_remove_software_node().
> > > > > 
> > > > > Of course my patch won't fix this issue.
> > > > > 
> > > > > I have heard that Heikki is looking how to fix the issue in your case and
> > > > > potentially in any other cases where device_add_software_node() is called
> > > > > against not formed object instance.
> > > > 
> > > > Dominik, can you test the attached patch to confirm if this really is
> > > > the case.
> > > 
> > > With this patch applied, the panic disappears.
> > 
> > Thanks Dominik. I'll clean it and send it out today.
> 
> Before I send the patch to Rafael and Greg, can you confirm that the
> appropriate API (device_is_registered()) also works? I'm attaching
> patch that should be the final version (if it works).

Heikki, that works perfectly. Many thanks, especially for the speedy
development of the bugfix!

Best,
	Dominik