[PATCH] tracing/core: Add current context on tracing recursion warning

[Frederic Weisbecker <fweisbec@gmail.com>]

On Sun, Apr 19, 2009 at 02:34:32PM +0200, Frederic Weisbecker wrote:
> On Sun, Apr 19, 2009 at 02:14:54PM +0800, Li Zefan wrote:
> > Frederic Weisbecker wrote:
> > > Hi,
> > > 
> > > Here is the v3 of the __string() field patchset.
> > > It applies suggestions from Steven and Peter with some arrangements.
> > > 
> > > This time, filtering is not supported (though it is ready in a pending patch).
> > > I wanted to provide it but it looks like filtering has been broken recently.
> > > Once I set a usual string filter, no more traces appear, and clearing it
> > > doesn't change anything.
> > > 
> > 
> > I tried it, and triggered a WARNING, and ring buffers was
> > disabled permanently:
> 
> 
> I've also seen this warning but on another event.
> I don't think this is related to this patchset but
> more about the tracing recursion detection.
> 
> For exemple, here we are in an Irq event, which doesn't
> use the __string() thing. For such off-case, the only change
> is a variable declaration and a + 0 operation.
> 
> Another thing: I've only seen it in a selftest.


Worst: I can't reproduce it anymore.
What were you doing when you got such warning? Were you
in a selftest, or trying a usual event?

Also, could you test the following patch. It will give us
more informations about the tracing recursion.

You can find it on:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing tracing/recursion

It's against tip/tracing/core

Thanks!

---
>From d13bf59ca011b976c561f623e3189a4a5b94370e Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Sun, 19 Apr 2009 15:30:19 +0200
Subject: [PATCH] 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.

[ Impact: more information in tracing recursion ]

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/trace/ring_buffer.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b421b0e..27a6e7d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1493,8 +1493,21 @@ static int trace_recursive_lock(void)
 	level = trace_irq_level();
 
 	if (unlikely(current->trace_recursion & (1 << level))) {
+		static atomic_t warned;
+
 		/* Disable all tracing before we do anything else */
 		tracing_off_permanent();
+
+		if (atomic_inc_return(&warned) == 1) {
+			printk(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);
 		return -1;
 	}
-- 
1.6.1