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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Wed, 11 Jul 2018 19:56:02 +0200
Message-ID: <CAKMK7uFuZ6NJOKHG6PRNLUytE4m6ZUdMakwLx9Ns39OwvTneWQ@mail.gmail.com>
Subject: Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Thomas Zimmermann <tzimmermann@suse.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Petr Mladek <pmladek@suse.com>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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On Wed, Jul 11, 2018 at 7:35 PM, Hans de Goede <hdegoede@redhat.com> wrote:
> Hi,
>
>
> On 11-07-18 17:42, Daniel Vetter wrote:
>>
>> On Wed, Jul 11, 2018 at 5:35 PM, Hans de Goede <hdegoede@redhat.com>
>> wrote:
>>>
>>> Hi,
>>>
>>> On 11-07-18 17:28, Daniel Vetter wrote:
>>>>
>>>>
>>>> On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede <hdegoede@redhat.com>
>>>> wrote:
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> On 11-07-18 17:07, Thomas Zimmermann wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> Hi
>>>>>>
>>>>>> Am 11.07.2018 um 16:52 schrieb Steven Rostedt:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> What if you make lockless_register_fb visible to fbcon, and then we
>>>>>>> can
>>>>>>> have a macro:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> There are more of these macro invocations under drivers/tty/vt, which
>>>>>> also mess up the log during debugging.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Hmm, so this option is already broken (in a way) then, my first
>>>>> reaction
>>>>> to your mail was that we should just remove that option. But that
>>>>> seemed
>>>>> a bit harsh to me so I've been working on a fix for the last 10 minutes
>>>>> or so.
>>>>>
>>>>> But if it is already broken I'm tempted to just remove the option and
>>>>> be done with it.  We really need less cruft in the fbdev/fbcon code not
>>>>> more.
>>>>
>>>>
>>>>
>>>> Please don't remove it, it makes debugging kms driver issues on
>>>> initial modeset (which is usually run from framebuffer_register, while
>>>> hodling the console_lock) impossible.
>>>
>>>
>>>
>>> OK, so if we don't remove it, we should probably make it so that it
>>> can be used without triggering any WARN_ONs, which would require changing
>>> the existing WARN_CONSOLE_UNLOCKED() so that the calls from
>>> drivers/tty/vt/vt.c
>>> also do not trigger it ?
>>>
>>> I guess one can just ignore the oopses when debugging, but debugging
>>> surely
>>> would be easier if there are just no oopses ?
>>
>>
>> I'd say let's only bother with the ones in fbcon.c. Avoids the trouble
>> with having to expose the fb module option to vt.c somehow.
>
>
> The plan was actually do the things the other way around, add a flag to
> vt.c which when set disables the WARN_ON calls and then have fbdev[.ko]
> set that when the fb.lockless_fb_register option is set.
>
>> The ones
>> in vt.c are as old as the git history (from a quick check at least),
>> and in my debugging they never have been annoying (or I somehow didn't
>> ever hit them, not idea).
>
>
> There is a #if 1 #define #else #define empty around the
> WARN_CONSOLE_UNLOCKED()
> call in include/linux/console.h I've the feeling that is there as a hack
> to be able to quickly disable the WARN_ONs when debugging.
>
> Have you seen Steven's suggestion which he send about the same time
> as your mail I'm replying to here ? I personally think that doing
> something like that makes sense (for as long as we have the need
> for the lockless_fb_register debug hack).
>
> Note I've 2 patches ready to go to only fix this in fbcon.c, but I
> think a more thorough fix makes sense.

Yeah Steven's suggestion looks reasonable to fix this all for good.
The #if 1 predates git history, so no idea why it was added or by whom
:-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch