linux-kernel - Re: [PATCH] vt/console: try harder to print output when panicing

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Message-Id: <20100623133637.fbb318e2.akpm@linux-foundation.org>
Date:	Wed, 23 Jun 2010 13:36:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Dave Airlie <airlied@...il.com>, linux-fbdev@...r.kernel.org,
	dri-devel@...ts.sf.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vt/console: try harder to print output when panicing

On Wed, 23 Jun 2010 13:05:47 -0700
Jesse Barnes <jbarnes@...tuousgeek.org> wrote:

> On Wed, 23 Jun 2010 12:56:05 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Wed, 23 Jun 2010 13:12:59 +1000
> > Dave Airlie <airlied@...il.com> wrote:
> > 
> > > Jesse's initial patch commit said:
> > > 
> > > "At panic time (i.e. when oops_in_progress is set) we should try a bit
> > > harder to update the screen and make sure output gets to the VT, since
> > > some drivers are capable of flipping back to it.
> > > 
> > > So make sure we try to unblank and update the display if called from a
> > > panic context."
> > > 
> > > I've enhanced this to add a flag to the vc that console layer can set
> > > to indicate they want this behaviour to occur. This also adds support
> > > to fbcon for that flag and adds an fb flag for drivers to indicate
> > > they want to use the support. It enables this for KMS drivers.
> > 
> > Interesting.  Getting real oops traces from machines running X will
> > make Rusty happy, and that's what we're all here for.
> > 
> > How well does this all work?  How reliable is it?  What's the success rate?
> > 
> > 
> > 
> > What's the downside here?  After all, not all oopses are catastrophic -
> > sometimes the machine will go blurt and keep running so the user can
> > take a look in the logs then perform an orderly reboot, etc.  As I
> > understand it, those non-catastrophic oopses will now flip the machine
> > from X and into the vt display, yes?  Can the user get it back to X
> > mode?
> 
> No, we'll only flip from the panic notifier chain.

So we still don't get to see the output from BUGs and random oopses?  I
don't think panics are all that common.

So am I correct in believing that if a user is getting invisible-oopses
then he can set /proc/sys/kernel/panic_on_oops, and then the oops
should be visible?

(Shouldn't all this stuff be explained in the changlog?)


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