linux-kernel - Re: [RFC] Try a bit harder to get output on the screen at panic time

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Date:	Sun, 30 May 2010 17:48:14 +0300
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Airlie <airlied@...il.com>,
	James Simmons <jsimmons@...radead.org>
Subject: Re: [RFC] Try a bit harder to get output on the screen at panic
 time

On Sat, 2010-05-22 at 01:26 +0300, Maxim Levitsky wrote: 
> On Fri, 2010-05-21 at 15:02 -0700, Jesse Barnes wrote: 
> > On Sat, 22 May 2010 00:57:30 +0300
> > Maxim Levitsky <maximlevitsky@...il.com> wrote:
> > 
> > > On Fri, 2010-05-21 at 00:14 +0300, Maxim Levitsky wrote: 
> > > > On Thu, 2010-05-20 at 09:28 -0700, Jesse Barnes wrote: 
> > > > > On Thu, 20 May 2010 04:27:07 +0300
> > > > > Maxim Levitsky <maximlevitsky@...il.com> wrote:
> > > > > 
> > > > > > On Thu, 2010-05-20 at 04:13 +0300, Maxim Levitsky wrote: 
> > > > > > > On Wed, 2010-05-19 at 17:34 -0700, Jesse Barnes wrote: 
> > > > > > > > On Fri, 9 Apr 2010 15:10:50 -0700
> > > > > > > > Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> > > > > > > > 
> > > > > > > > > This set of 3 patches makes it a little more likely we'll get panic
> > > > > > > > > output onto the screen even when X is running, assuming a KMS enabled
> > > > > > > > > stack anyway.
> > > > > > > > > 
> > > > > > > > > It gets me from a blank or very sparsely populated black screen at
> > > > > > > > > panic time, to one including the full backtrace and panic output at
> > > > > > > > > panic time (tested with "echo c > /proc/sysrq-trigger" from an X
> > > > > > > > > session).
> > > > > > > > > 
> > > > > > > > > It doesn't cover every case; for instance I think it'll fail when X has
> > > > > > > > > disabled the display, but those cases need to be handled with separate
> > > > > > > > > patches anyway (need to add atomic DPMS paths for instance).
> > > > > > > > > 
> > > > > > > > > Anyway, please test these out and let me know if they work for you.
> > > > > > > > 
> > > > > > > > Ping Linus & Dave again.  Have you guys tried these?  Really, it's cool.
> > > > > > > > 
> > > > > > > Second that, just tested these patches, and these work perfectly.
> > > > > > > One more reason for me to dump nvidia driver for nouveau.
> > > > > > 
> > > > > > 
> > > > > > Unfortunately I spoke too soon.
> > > > > > 
> > > > > > 
> > > > > > After suspend to ram, system doesn't properly resume now.
> > > > > > 
> > > > > > My system is based on nvidia G86, I use latest nouveau drivers, and
> > > > > > suspend with compiz running.
> > > > > > 
> > > > > > I also patched kernel not to do vt switch on suspend/resume:
> > > > > > 
> > > > > > diff --git a/drivers/gpu/drm/nouveau/nouveau_state.c
> > > > > > b/drivers/gpu/drm/nouveau/nouveau_state.c
> > > > > > index 062b7f6..b3ef08b 100644
> > > > > > --- a/drivers/gpu/drm/nouveau/nouveau_state.c
> > > > > > +++ b/drivers/gpu/drm/nouveau/nouveau_state.c
> > > > > > @@ -31,6 +31,7 @@
> > > > > > #include "drm_crtc_helper.h"
> > > > > > #include <linux/vgaarb.h>
> > > > > > #include <linux/vga_switcheroo.h>
> > > > > > +#include <linux/suspend.h>
> > > > > > 
> > > > > > #include "nouveau_drv.h"
> > > > > > #include "nouveau_drm.h"
> > > > > > @@ -771,6 +772,8 @@ int nouveau_load(struct drm_device *dev, unsigned
> > > > > > long flags)
> > > > > >                 int ret = nouveau_card_init(dev);
> > > > > >                 if (ret)
> > > > > >                         return ret;
> > > > > > +
> > > > > > +               pm_set_vt_switch(0);
> > > > > >         }
> > > > > > 
> > > > > >         return 0;
> > > > > 
> > > > > Hm I don't see how my patches would have affected suspend/resume, since
> > > > > they just add "oops_in_progress" checks to a few places.  Are you sure
> > > > > something else isn't breaking your resume path?
> > > > I am sure. I just reverted them, and everything works again.
> > > > I refer to 3 patches in this thread.
> > > In fact I might look a bit silly, but I applied these patches on top of
> > > linus master tree + nouveau master, and suspend to ram works just fine.
> > > 
> > > Maybe it shows up when kgdb+kdb isn't compiled in or so.
> > > Maybe it just triggered some bug in nouveau drivers...
> > > 
> > > 
> > > (Note that I also enabled kgdb, and kdb, and breaking into kdb (SysRQ+g)
> > > doesn't switch console mode, just hangs till I press 'g'.
> > 
> > Ok so it sounds like these particular patches are innocent?
> > 
> > As for kdb, I think the latest tree is probably missing the graphics
> > switch support on the driver side...
> In what part? nouveau or kdb?
> 
> Screen does switch to text mode and displays the backtrace on 'panic'
> (Tested with sysrq+c).
> (If kdb is enabled, screen doesn't switch, but allowing kdb to continue
> via 'g' command eventually breaks into it.)

Ping.

Best regards,
Maxim Levitsky

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