linux-kernel - Re: [PATCH] drm: inhibit drm drivers register to uninitialized drm core

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Date:   Tue, 11 Jul 2017 11:41:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Alexandru Moise <00moses.alexander00@...il.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Jessica Yu <jeyu@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Dave Airlie <airlied@...ux.ie>,
        Sean Paul <seanpaul@...omium.org>,
        "Nikula, Jani" <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH] drm: inhibit drm drivers register to uninitialized drm
 core

On Mon, Jul 10, 2017 at 08:00:37PM +0200, Daniel Vetter wrote:
> On Mon, Jul 10, 2017 at 9:14 AM, Alexandru Moise
> <00moses.alexander00@...il.com> wrote:
> > On Mon, Jul 10, 2017 at 08:52:46AM +0200, Daniel Vetter wrote:
> >> On Sat, Jul 08, 2017 at 11:43:52PM +0200, Alexandru Moise wrote:
> >> > If the DRM core fails to init for whatever reason, ensure that
> >> > no driver ever calls drm_dev_register().
> >> >
> >> > This is best done at drm_dev_init() as it covers drivers that call
> >> > drm_dev_alloc() as well as drivers that prefer to embed struct
> >> > drm_device into their own device struct and call drm_dev_init()
> >> > themselves.
> >> >
> >> > In my case I had so many dynamic device majors used that the major
> >> > number for DRM (226) was stolen, causing DRM core init to fail after
> >> > failing to register a chrdev, and ultimately calling debugfs_remove()
> >> > on drm_debugfs_root in drm_core_exit().

Note, there are patches in my "to-apply" queue to prevent that from
happening, that should show up in 4.14-rc1.  So that shouldn't be an
issue in the future.

> I feared that would be the answer :-/ Still feels funny that everyone
> will need to hand-roll this, or does everyone simply assume that their
> subsystem's module_init never fails?

How would we not "hand-roll" this?  Every subsystem works a bit
differently.  But if you can think of a way to make this generic, that
would be great...

thanks,

greg k-h