linux-kernel - Re: problem with function

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Message-ID: <4A3ADBFA.1060702@goop.org>
Date:	Thu, 18 Jun 2009 17:29:46 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Jake Edge <jake@....net>, LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: problem with function_graph self-test?

On 06/17/09 20:24, Steven Rostedt wrote:
> On Tue, 16 Jun 2009, Jake Edge wrote:
>
>   
>> Hi Steve,
>>
>> This has taken me a bit to track down ... I built a kernel from Linus's
>> git tree (as of this morning: commit
>> 03347e2592078a90df818670fddf97a33eec70fb) and when i boot it, it locks
>> up hard giving me a cursor in the upper left (which seems to grow then
>> shrink once, if that tells anyone anything) and no other output ... i
>> started messing with kernel params (turning off quiet, rhgb, adding
>> boot_delay and, eventually figuring out i needed lpj as well) to try
>> and extract some info ... it seems to reliably fail in the
>> function_graph tracer self-test with a variety of messages (I
>> unfortunately don't have a serial console on the laptop that I am
>> using) ... two of the messages that I got (possibly from different
>> boots):
>>
>> BUG: unable to handle kernel NULL pointer dereference at 00000048
>> BUG: Function graph tracer hang!
>>
>> I can try and get more information, but I wanted to check first if you
>> already know about this ... somehow i'll either need to type faster :)
>> or reliably slow it down and take pictures, which I can do if you'd
>> like ...
>>
>> obviously, for my purposes, i can turn off the selftests and/or the
>> function_graph tracer ...
>>     
>
> Jake, when you find a bug, you really find a bug!
>
> This is something that gcc is screwing with us. After spending all day 
> today trying to figure out what is happening, I finally found it in the 
> assembly.
>
> In the timer_stats_update_stats function, I get this at the beginning:
>
> 00000327 <timer_stats_update_stats>:
>  327:   57                      push   %edi
>  328:   8d 7c 24 08             lea    0x8(%esp),%edi
>  32c:   83 e4 e0                and    $0xffffffe0,%esp
>  32f:   ff 77 fc                pushl  0xfffffffc(%edi)
>  332:   55                      push   %ebp
>  333:   89 e5                   mov    %esp,%ebp
>  335:   57                      push   %edi
>  336:   56                      push   %esi
>  337:   53                      push   %ebx
>  338:   81 ec 8c 00 00 00       sub    $0x8c,%esp
>  33e:   e8 fc ff ff ff          call   33f <timer_stats_update_stats+0x18>
>                         33f: R_386_PC32 mcount
>
>
> And this at the end of the function:
>
>  4f6:   8d 67 f8                lea    0xfffffff8(%edi),%esp
>  4f9:   5f                      pop    %edi
>  4fa:   c3                      ret    
>   

Something to do with using _RET_IP_ in spin_unlock_irqrestore() perhaps?

    J
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