linux-kernel - Re: [rfc] disable scheduler warnings during oopses.

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Date:	Fri, 23 Dec 2011 13:06:00 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Airlie <airlied@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [rfc] disable scheduler warnings during oopses.

On Fri, 2011-12-23 at 11:19 +0100, Ingo Molnar wrote:
> * Dave Jones <davej@...hat.com> wrote:
> 
> > The panic-on-framebuffer code seems to cause a schedule
> > to occur during an oops. This causes a bunch of extra
> > spew as can be seen in https://bugzilla.redhat.com/attachment.cgi?id=549230
> > 
> > Would this (untested) patch be sufficient here, or does the drm
> > code need rearchitecting to not perform allocations during panic ?
> > 
> > Signed-off-by: Dave Jones <davej@...hat.com>
> > 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index d6b149c..627f788 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -4321,6 +4321,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
> >  {
> >  	struct pt_regs *regs = get_irq_regs();
> >  
> > +	if (oops_in_progress)
> > +		return;
> > +
> >  	printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
> >  		prev->comm, prev->pid, preempt_count());
> >  
> 
> Doing that makes sense - if an oops in going on we don't want to 
> produce recursive messages. Note that scheduler code has been 
> moved to kernel/sched/, so i've changed the patch accordingly.

Urgh I would actually argue against merging this. What the KSM console
does is horridly wrong, and simply papering over it doesn't help its
cause. Its up there with USB-Serial console on wrongness.

> Note that despite that, the DRM code *definitely* needs to be 
> fixed to not allocate and schedule while printing on the 
> framebuffer in KMS mode ...

For sure, its plain insane and completely unreliable.
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