linux-kernel - Re: Atomicity in KMS panic notifier

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Message-ID: <CANq1E4QkzqhrgeJrAZ=wxQR751BdSK13E4QjWPWkiq5B8vFr9Q@mail.gmail.com>
Date:	Tue, 6 May 2014 15:32:21 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Daniel Vetter <daniel@...ll.ch>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Atomicity in KMS panic notifier

Hi

On Tue, May 6, 2014 at 3:27 PM, Takashi Iwai <tiwai@...e.de> wrote:
> At Mon, 5 May 2014 16:52:45 +0200,
> Daniel Vetter wrote:
>>
>> On Mon, May 5, 2014 at 4:48 PM, Takashi Iwai <tiwai@...e.de> wrote:
>> >
>> > The current problem I see is that the rest of panic notifier chain
>> > won't be called once when we hit the problem in KMS notifier.  So,
>> > this bug in KMS influences on the rest panic behavior.
>> >
>> > Maybe a hackish solution would be to keep KMS notifier at the end of
>> > notifier chain so that it crashes at last.  I don't like this either,
>> > but...
>>
>> You need to do that with both the kms panic notifier in
>> drm_fb_helper.c and with the fbcon panic notifier. And iirc there's
>> also a console->unblank call somewhere which _also_ can end up in
>> ->set_par. But I'm not sure anymore when exactly that one is run, I've
>> tried hard to forget this all ;-)
>
> Looking back at the code again, it seems that fbcon has no panic
> notifier.  It has own notifier chain, but it's a private chain that
> isn't called by the panic.  So, we can forget about fbcon, at least (I
> hope).

fbcon is called through the VT or fbdev layer, which is called by
bust_spinlocks(1) via either unblank_screen() or console_unblank().

Cheers
David
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