linux-kernel - Re: resume from s2ram regression (bisected to ftrace...)

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Date:	Tue, 12 Aug 2008 18:37:28 +0200
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-pm@...ts.linux-foundation.org
Subject: Re: resume from s2ram regression (bisected to ftrace...)

On Mon, Aug 11, 2008 at 02:27:01PM -0400, Steven Rostedt wrote:
> Rafael J. Wysocki wrote:
>> On Sunday, 10 of August 2008, Marcin Slusarz wrote:
>>   
>>> On Sun, Aug 10, 2008 at 07:40:12PM +0200, Rafael J. Wysocki wrote:
>>>     
>>>> On Sunday, 10 of August 2008, Marcin Slusarz wrote:
>>>>       
>>>>> Hi
>>>>>
>>>>> Few days ago I discovered that resume from suspend to ram does not work 
>>>>> anymore
>>>>> on my 2.6.27-rc2 (actually 796aadeb1b2db9b5d463946766c5bbfd7717158c) 
>>>>> gentoo box.
>>>>> My computer just boots on resume. Today I had enough time to bisect it 
>>>>> and found
>>>>> (after 1 panic and 1 build breakage) out "the reason":
>>>>>
>>>>> $ git bisect good
>>>>> d05cdb25d80f06f77aa6bddb53cd1390d4d91a0b is first bad commit
>>>>> commit d05cdb25d80f06f77aa6bddb53cd1390d4d91a0b
>>>>> Author: Steven Rostedt <rostedt@...dmis.org>
>>>>> Date:   Mon May 12 21:20:54 2008 +0200
>>>>>
>>>>>     ftrace: fix dynamic ftrace selftest
>>>>>         
>>>> Does it still happen if:
>>>> - CONFIG_FTRACE is unset
>>>>       
>>> no
>>>
>>>     
>>>> - CONFIG_FTRACE is set, but CONFIG_FTRACE_STARTUP_TEST is unset?
>>>>       
>>> yes
>>>     
>>
>> Thanks for testing.
>>
>> Well, ftrace is a new feature in 2.6.27, IIRC, so this is not a regression 
>> in
>> the strict sense.
>>
>> Still, of couse, there is a bug in ftrace that needs to be fixed.  Steven?
>>   
> Sorry for the late response.
>
> Red Hat changed its mail servers, and my mail was in limbo for a while.
>
> I'm not doubting that FTRACE enabled breaks suspend to ram, but I find it 
> highly unlikely that the commit you posted was the culprit. Especially 
> since it still breaks when STARTUP_TEST is disabled. That change was a 
> STARTUP_TEST change only.  Perhaps it just moved things around enough to 
> cause your issues.
>
> But you say that if you take Linus's latest git tree, and revert only this 
> change, it works??

Yes.

> Hmm, this is very strange.

I agree. Any idea how to debug it?

Marcin
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