Date: Mon, 8 Apr 2013 18:08:11 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Tejun Heo <tj@kernel.org>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, mingo@redhat.com, x86@kernel.org,
        rth@twiddle.net, linux@arm.linux.org.uk, msalter@redhat.com,
        starvik@axis.com, dhowells@redhat.com, tony.luck@intel.com,
        benh@kernel.crashing.org, takata@linux-m32r.org, geert@linux-m68k.org,
        james.hogan@imgtec.com, monstr@monstr.eu, ralf@linux-mips.org,
        jonas@southpole.se, rkuo@codeaurora.org, schwidefsky@de.ibm.com,
        liqin.chen@sunplusct.com, davem@davemloft.net, lethal@linux-sh.org,
        vgupta@synopsys.com, chris@zankel.net, cmetcalf@tilera.com,
        ysato@users.sourceforge.jp, gxt@mprc.pku.edu.cn, jdike@addtoit.com
Subject: Re: [PATCH 1/7] x86: don't show trace beyond show_stack(NULL, NULL)
Message-ID: <20130408160811.GA20612@gmail.com>
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* Tejun Heo <tj@kernel.org> wrote:

> show_stack(current or NULL, NULL) is used to print the backtrace of
> the current task.  As trace beyond the function itself isn't of much
> interest to anyone, don't show it by determining sp and bp in
> show_stack()'s frame and passing them to show_stack_log_lvl().
> 
> This brings show_stack(NULL, NULL)'s behavior in line with
> dump_stack().
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> ---
>  arch/x86/kernel/dumpstack.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index c8797d5..dd1a7c3 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -176,7 +176,19 @@ void show_trace(struct task_struct *task, struct pt_regs *regs,
>  
>  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.

Would be nice to create an __always_inline helper for all this, and to use it for 
show_regs() as well.

Then the !bp special case in dump_trace() could be removed, and !bp be made an 
invalid variant.

Thanks,

	Ingo
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