linux-kernel - Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable

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Message-ID: <CAKMK7uG-xiCKkxhujL=J6n9ozYfW+fsioGHEmYRxpszVX=5PDg@mail.gmail.com>
Date:   Wed, 11 Jul 2018 17:28:33 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable

On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede <hdegoede@...hat.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.
-Daniel

>> WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
>> ...' construct [1]. I thought about turning this into a config option.
>
>
> Ah I noticed the #if but I did not notice that it was a "#if 1".
>
> If you want to fix lockless_register_fb it really should be replaced
> with a runtime check, not a Kconfig option. This would require having
> some lockless variable in the console code itself, which then gets
> set by the fbdev code during init based on its lockless_register_fb
> setting.
>
> But as said I think we should seriously consider just removing
> lockless_register_fb.
>
> Regards,
>
> Hans
>
>
>
>
>
>
>
>>
>> Best regards
>> Thomas
>>
>> [1]
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203
>>
>>>
>>> #define WARN_FB_CONSOLE_UNLOCKED()                      \
>>>         do {                                            \
>>>                 if (unlikely(!lockless_register_fb))    \
>>>                         WARN_CONSOLE_UNLOCKED();        \
>>>         } while (0)
>>>
>>> And use that instead?
>>>
>>> -- Steve
>>>
>>>
>>>> Best regards
>>>> Thomas
>>>>
>>>>> Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
>>>>> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
>>>>> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
>>>>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>>>>> ---
>>>>> Changes in v3:
>>>>> -New patch in v3 of this patchset
>>>>>
>>>>> Changes in v4:
>>>>> -Keep the comments about which fbcon functions need locks in place
>>>>> ---
>>>>>   drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
>>>>>   1 file changed, 11 insertions(+)
>>>>>
>>>>> diff --git a/drivers/video/fbdev/core/fbcon.c
>>>>> b/drivers/video/fbdev/core/fbcon.c
>>>>> index c910e74d46ff..cd8d52a967aa 100644
>>>>> --- a/drivers/video/fbdev/core/fbcon.c
>>>>> +++ b/drivers/video/fbdev/core/fbcon.c
>>>>> @@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int
>>>>> user)
>>>>>         struct fb_info *oldinfo = NULL;
>>>>>         int found, err = 0;
>>>>>   +     WARN_CONSOLE_UNLOCKED();
>>>>> +
>>>>>         if (oldidx == newidx)
>>>>>                 return 0;
>>>>>   @@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
>>>>>   {
>>>>>         int i, new_idx = -1, ret = 0;
>>>>>   +     WARN_CONSOLE_UNLOCKED();
>>>>> +
>>>>>         if (!fbcon_has_console_bind)
>>>>>                 return 0;
>>>>>   @@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info
>>>>> *info)
>>>>>   {
>>>>>         int i, idx;
>>>>>   +     WARN_CONSOLE_UNLOCKED();
>>>>> +
>>>>>         idx = info->node;
>>>>>         for (i = first_fb_vc; i <= last_fb_vc; i++) {
>>>>>                 if (con2fb_map[i] == idx)
>>>>> @@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info
>>>>> *info)
>>>>>   static void fbcon_remap_all(int idx)
>>>>>   {
>>>>>         int i;
>>>>> +
>>>>> +       WARN_CONSOLE_UNLOCKED();
>>>>> +
>>>>>         for (i = first_fb_vc; i <= last_fb_vc; i++)
>>>>>                 set_con2fb_map(i, idx, 0);
>>>>>   @@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info
>>>>> *info)
>>>>>   {
>>>>>         int ret = 0, i, idx;
>>>>>   +     WARN_CONSOLE_UNLOCKED();
>>>>> +
>>>>>         idx = info->node;
>>>>>         fbcon_select_primary(info);
>>>>>
>>>>
>>>>
>>>
>>
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> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel


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

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