linux-kernel - Re: [git pull] ftrace for v2.6.27

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Message-ID: <20080813071905.GA18529@elte.hu>
Date:	Wed, 13 Aug 2008 09:19:05 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Bruce Duncan <bwduncan@...il.com>
Cc:	linux-kernel@...r.kernel.org, Steven Rostedt <srostedt@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [git pull] ftrace for v2.6.27


* Bruce Duncan <bwduncan@...il.com> wrote:

> Hi Ingo, Steven, everyone,
> 
> [ Please CC me in replies ]
> 
> I have just tracked down a regression in 2.6.27-rc2 wrt 2.6.26. Commit 
> 77a2b37d227483fe52aead242652aee406c25bf0 (ftrace: startup tester on 
> dynamic tracing.) causes my laptop to fail to resume from S3 (it 
> simply reboots about a second after the resume starts and the display 
> never shows anything).
> 
> The patch doesn't revert with patch -R (I don't know if there's a 
> cleverer way to ask git to revert it), but the problem goes away if I 
> turn off CONFIG_DYNAMIC_FTRACE.
> 
> The commit and bisect log are attached. Please can you help me to 
> debug this?

could you please send your .config file as well?

Suspend+resume bugs are notoriously hard to debug (there's no console 
output in most cases), so i guess the best way to debug this is for 
Steve or me to try to reproduce it. Could you send the output of this 
script:

  http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh

that will tell us what kind of hw you have.

and could you perhaps try the patch below? The patch disables on the fly 
dynamic code patching - which is the primary suspect here. If it makes a 
difference on your box then a theory would be that ftraced runs too soon 
after suspend+resume.

	Ingo

----------------------->
Subject: ftrace: debug
From: Ingo Molnar <mingo@...e.hu>
Date: Wed Aug 13 09:17:12 CEST 2008

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/trace/ftrace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/kernel/trace/ftrace.c
===================================================================
--- linux.orig/kernel/trace/ftrace.c
+++ linux/kernel/trace/ftrace.c
@@ -811,7 +811,7 @@ static int ftraced(void *ignore)
 		/* check once a second */
 		schedule_timeout(HZ);
 
-		if (unlikely(ftrace_disabled))
+		if (1)
 			continue;
 
 		mutex_lock(&ftrace_sysctl_lock);
--
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