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

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Date:	Wed, 13 Aug 2008 17:18:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	Bruce Duncan <bwduncan@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [git pull] ftrace for v2.6.27


* Steven Rostedt <srostedt@...hat.com> wrote:

> Bruce Duncan 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?
>>
>>
>>   
>
> I found that I have a box that displays this bug. Without FTRACE it 
> suspends and resumes fine. With FTRACE enabled, it does not.
>
> I'll be actively debugging it now. (unfortunately, as with all new 
> laptops, I don't have a serial for it).

try latest tip/master plus an USB debug key, then enable 
CONFIG_EARLY_PRINTK_DBGP=y in your .config on the host, add the 
earlyprintk=dbgp,keep boot parameter and reboot [and disable USB for 
good measure]. On the other host you connect to via an USB cable, enable 
USB_SERIAL_DEBUG=y and use /dev/ttyUSB0 with the serial terminal app of 
your choice.

that, as long as the USB ports are operational, gives a working serial 
console on just about any laptop.

	Ingo
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