linux-kernel - Re: drm/mgag200: doesn't work in panic context

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Message-ID: <20150629094215.GD12383@pd.tnic>
Date:	Mon, 29 Jun 2015 11:42:16 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	"Wang, Rui Y" <rui.y.wang@...el.com>,
	Dave Airlie <airlied@...hat.com>,
	"Clark, Rob" <robdclark@...il.com>,
	"Roper, Matthew D" <matthew.d.roper@...el.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: drm/mgag200: doesn't work in panic context

On Mon, Jun 29, 2015 at 11:25:17AM +0200, Daniel Vetter wrote:
> As long as the display is up and running we should have a fair stab at
> showing the oops

Yeah, that has the same problem as all the other methods for showing
oops - *if* it is still healthly. Like, for example, trying to catch an
oops in networking with netconsole :)

> - it's just that no one has seriously bothered with the necessary
> infastructure, automated testing (it won't work otherwise) and driver
> work.

Right.

> drm_fb_helper_panic isn't the only panic handler - fbdev/fbcon have
> their own. They interfere, and fbdev blissfully assumes that it can
> call almost any driver hook from hardirq context. Which means you'd
> also need to consolidate the various hand-rolled (in drivers instead
> of the fbdev helper) bits to offload fbdev callbacks to workers and
> make sure we don't go boom in panics in there either.

Hmmm, this would mean to go and tell them through the panic notifier
to not do anything "risky" anymore. Perhaps even stop them from doing
regular tasks which could become risky in the case of panic. I guess
this would mean, we should be doing the same in other subsystems too.

Hmm.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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