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

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Message-ID: <CAKMK7uGPjRAGdahX-T9PBPRw_pCx2dDy3HOHxRQ0Dwf_jVbfzA@mail.gmail.com>
Date:   Tue, 11 Jul 2017 12:02:52 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 Tue, Jul 11, 2017 at 11:41 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> 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...

Well there's so much almost-magic helper/support code that very often
just asking the right people gives me the answer. Sounds like this is
a case where we haven't yet invented that magic, and I don't have a
bright idea either. I'll Apply Alex' patch.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch