linux-kernel - Re: [PATCH] tracing/core: Add current context on tracing recursion warning

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Date:	Sun, 19 Apr 2009 20:45:51 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] tracing/core: Add current context on tracing recursion
	warning


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Sun, Apr 19, 2009 at 04:01:54PM +0200, Ingo Molnar wrote:
> > It would be nice to have this ... but there's no need to do that 
> > atomic thing - just use printk_once() please. (if we race with 
> > another instance and get two messages that's not a problem)
> > 
> > 	Ingo
> 
> 
> Ah, indeed I forgot about printk_once()
> I've updated the repo with the following v2 on:
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing tracing/recursion
> 
> ---
> >From e894732989e345ea012de146c37d71dd7ed3575d Mon Sep 17 00:00:00 2001
> From: Frederic Weisbecker <fweisbec@...il.com>
> Date: Sun, 19 Apr 2009 16:18:16 +0200
> Subject: [PATCH v2] tracing/core: Add current context on tracing recursion warning

> 
> In case of tracing recursion detection, we only get the stacktrace.
> But the current context may be very useful to debug the issue.
> 
> This patch adds the softirq/hardirq/nmi context with the warning
> using lockdep context display to have a familiar output.
> 
> v2: Use printk_once()
> 
> [ Impact: more information in tracing recursion ]
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/trace/ring_buffer.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index b421b0e..e315178 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1495,6 +1495,16 @@ static int trace_recursive_lock(void)
>  	if (unlikely(current->trace_recursion & (1 << level))) {
>  		/* Disable all tracing before we do anything else */
>  		tracing_off_permanent();
> +
> +		printk_once(KERN_WARNING "Tracing recursion: "
> +			    "[HC%u[%lu]:SC%u[%lu]:NMI[%lu]:HE%u:SE%u]\n",
> +			    current->hardirq_context,
> +			    hardirq_count() >> HARDIRQ_SHIFT,
> +			    current->softirq_context,
> +			    softirq_count() >> SOFTIRQ_SHIFT,
> +			    in_nmi(), current->hardirqs_enabled,
> +			    current->softirqs_enabled);
> +
>  		WARN_ON_ONCE(1);

Pulled, thanks Frederic!

btw., we might have done it via:

	if (WARN_ON_ONCE(1)) {
		printk(...);
	}

as well ... but i have not checked how WARN_ON_ONCE() return value 
behaves after the first warning - does it return true or false?

	Ingo
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