linux-kernel - Re: [PATCH] MIPS: Makefile: workaround printk recursion bug

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Date:	Thu, 11 Apr 2013 09:46:39 +0200
From:	Wladislav Wiebe <wladislav.kw@...il.com>
To:	David Daney <ddaney.cavm@...il.com>
CC:	ralf@...ux-mips.org, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Makefile: workaround printk recursion bug

Hi,

On 10/04/13 18:37, David Daney wrote:
> On 04/10/2013 02:12 AM, Wladislav Wiebe wrote:
>>
>> From: Wladislav Wiebe <wladislav.kw@...il.com>
>>
>> Function tracing is broken due to removal of selecting FRAME_POINTER with
>> FUNCTION_TRACER as result of commit: b732d439cb43336cd6d7e804ecb2c81193ef63b0
>>
>> Latest commit ad8c396936e328f5344e1881afde9e28d5f2045f "MIPS: Unbreak
>> function tracer for 64-bit kernel." fixes just the early startup hang,
>> but on MIPS64/CAVIUM_OCTEON2 are still random printk recursion bugs
>> which cause also Kernel hangs, especially on late startup phase when
>> network drivers get loaded. This patch enable for CAVIUM_OCTEON2/64 Bit
>> architecture -fno-omit-frame-pointer cflag when FUNCTION_TRACER get
>> enabled. This will fix random Kernel hangs with "BUG: recent printk
>> recursion!" from linux/kernel/printk.c.
>>
>> Maybe there exist a other solution in mcount handling, since in the
>> commit message from Al Cooper is mentioned that "MIPS frame pointers are
>> generally considered to be useless because they cannot be used to unwind
>> the stack. Unfortunately the MIPS function tracing code has bugs that
>> are masked by the use of frame pointers. This commit fixes the bugs so
>> that MIPS frame pointers don't need to be enabled."
>>
>> But this is just a solution for MIPS32 - on a symmetric multiprocessing
>> @MIPS64/CAVIUM_OCTEON2 it doesn't work properly.
> 
> There are a couple of problems that I see with this patch:
> 
> 1) It doesn't handle non-OCTEON2.  Surely other 64-bit targets are effected as well
> 
> 2) You don't say how it is broken or how this fixes it.
> 
> 3) Function graph tracing on 3.9.0-rc6 compiled with gcc-4.7.0 works fine for me without this.  So I see no need to clog up the make files with a rats nest of ifdef

well, didn't cross checked with gcc-4.7.0 (currently using gcc-4.3).
Will do so and get back if problem still visible.

Thanks!


> 
> Without more information about why this  is needed, I would have to say NAK.
> 
> David Daney
> 
>>
>> Signed-off-by: Wladislav Wiebe <wladislav.kw@...il.com>
>> ---
>>   arch/mips/Makefile |    9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
>> index 6f7978f..8befe31 100644
>> --- a/arch/mips/Makefile
>> +++ b/arch/mips/Makefile
>> @@ -119,6 +119,15 @@ cflags-$(CONFIG_SB1XXX_CORELIS)    += $(call cc-option,-mno-sched-prolog) \
>>                      -fno-omit-frame-pointer
>>
>>   #
>> +# FTrace depended compiler options, currently only needed by MIPS64/OCTEON2.
>> +#
>> +ifdef CONFIG_64BIT
>> +ifdef CONFIG_CAVIUM_OCTEON2
>> +cflags-$(CONFIG_FUNCTION_TRACER) += $(call cc-option,-fno-omit-frame-pointer)
>> +endif
>> +endif
>> +
>> +#
>>   # CPU-dependent compiler/assembler options for optimization.
>>   #
>>   cflags-$(CONFIG_CPU_R3000)    += -march=r3000
>>
> 

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