linux-kernel - Re: [PATCH 1/7] x86: don't show trace beyond show

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Date:	Wed, 10 Apr 2013 12:35:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mingo@...hat.com, x86@...nel.org,
	rth@...ddle.net, linux@....linux.org.uk, msalter@...hat.com,
	starvik@...s.com, dhowells@...hat.com, tony.luck@...el.com,
	benh@...nel.crashing.org, takata@...ux-m32r.org,
	geert@...ux-m68k.org, james.hogan@...tec.com, monstr@...str.eu,
	ralf@...ux-mips.org, jonas@...thpole.se, rkuo@...eaurora.org,
	schwidefsky@...ibm.com, liqin.chen@...plusct.com,
	davem@...emloft.net, lethal@...ux-sh.org, vgupta@...opsys.com,
	chris@...kel.net, cmetcalf@...era.com, ysato@...rs.sourceforge.jp,
	gxt@...c.pku.edu.cn, jdike@...toit.com
Subject: Re: [PATCH 1/7] x86: don't show trace beyond show_stack(NULL, NULL)


* Tejun Heo <tj@...nel.org> wrote:

> Hello, Ingo.
> 
> On Mon, Apr 08, 2013 at 06:08:11PM +0200, Ingo Molnar wrote:
> > >  void show_stack(struct task_struct *task, unsigned long *sp)
> > >  {
> > > -	show_stack_log_lvl(task, NULL, sp, 0, "");
> > > +	unsigned long bp = 0;
> > > +	unsigned long stack;
> > > +
> > > +	/*
> > > +	 * Stack frames below this one aren't interesting.  Don't show them
> > > +	 * if we're printing for %current.
> > > +	 */
> > > +	if (!sp && (!task || task == current)) {
> > > +		sp = &stack;
> > > +		bp = stack_frame(current, NULL);
> > > +	}
> > > +
> > > +	show_stack_log_lvl(task, NULL, sp, bp, "");
> > 
> > Hm, show_regs() has a similar problem AFAICS.
> 
> Doesn't seem so.  show_regs() have pt_regs which gets passed to
> dump_trace() and then used to determine the frame being dumped.
> e.g. BUG() takes pt_regs from the faulting frame and thus doesn't show
> anything beyond it.

Ok - but my other observation probably holds, that the bp == 0 special case in 
dump_trace() should be changed to a [printk()-ed] warning or so? No user will pass 
in bp == 0 legitimately, AFAICS.

Thanks,

	Ingo
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