linux-kernel - [ 006/187] powerpc/ftrace: Do not trace restore

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Date:	Thu, 12 Jul 2012 15:32:42 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Steven Rostedt <rostedt@...dmis.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [ 006/187] powerpc/ftrace: Do not trace restore_interrupts()

From: Greg KH <gregkh@...uxfoundation.org>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Steven Rostedt <rostedt@...dmis.org>

commit 2d773aa4810d4a612d1c879faacc38594cc3f841 upstream.

As I was adding code that affects all archs, I started testing function
tracer against PPC64 and found that it currently locks up with 3.4
kernel. I figured it was due to tracing a function that shouldn't be, so
I went through the following process to bisect to find the culprit:

 cat /debug/tracing/available_filter_functions > t
 num=`wc -l t`
 sed -ne "1,${num}p" t > t1
 let num=num+1
 sed -ne "${num},$p" t > t2
 cat t1 > /debug/tracing/set_ftrace_filter
 echo function /debug/tracing/current_tracer
 <failed? bisect t1, if not bisect t2>

It finally came down to this function: restore_interrupts()

I'm not sure why this locks up the system. It just seems to prevent
scheduling from occurring. Interrupts seem to still work, as I can ping
the box. But all user processes freeze.

When restore_interrupts() is not traced, function tracing works fine.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/kernel/irq.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -277,7 +277,7 @@ EXPORT_SYMBOL(arch_local_irq_restore);
  * NOTE: This is called with interrupts hard disabled but not marked
  * as such in paca->irq_happened, so we need to resync this.
  */
-void restore_interrupts(void)
+void notrace restore_interrupts(void)
 {
 	if (irqs_disabled()) {
 		local_paca->irq_happened |= PACA_IRQ_HARD_DIS;


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