linux-kernel - Re: 2.6.39-rc6-mmotm0506 and -next - __kfree

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Date:	Wed, 11 May 2011 08:52:53 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Valdis.Kletnieks@...edu
CC:	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.39-rc6-mmotm0506 and -next - __kfree_rcu breaks third-party
 kernel code

On 05/10/2011 12:56 AM, Valdis.Kletnieks@...edu wrote:
> On Mon, 09 May 2011 09:17:57 PDT, Randy Dunlap said:
> 
>> I'd be happy to see a simple fix, but we don't generally support building
>> external modules without using the kernel kbuild infrastructure AFAIK --
>> and when I add a Makefile along with your kernconf.c file, it builds successfully
>> on mmotm-2011-0506-1639.
> 
> And in fact the module *does* use the Makefile stuff for the actual build - it
> was just the installer's "am I looking at a sane 2.6 tree" sanity check that
> bombed. So I go looking for what special sauce the Makefile adds to make it
> work, and....
> 
> OK, *now* I'm confused.  The magic sauce appears to be "-Os". Adding that makes
> the compile work.  And for no obvious reason - there's something in there that
> causes indigestion, but only if the optimizer isn't invoked.
> 
> *WTF*?
> 
>  LANG=C ./kern.sh 
> cat > /tmp/kernconf.c <<EOF
> #include <linux/version.h>
> #include <linux/utsname.h>
> EOF
> + cat
> 
> kern="/lib/modules/2.6.39-rc6-mmotm0506/"
> + kern=/lib/modules/2.6.39-rc6-mmotm0506/
> cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I${kern}/build/include -I$kern/arch/x86/include/generated -include ${kern}/build/include/generated/autoconf.h -I${kern}/build/arch/x86/include -I${kern}/include/generated -Os -c /tmp/kernconf.c
> + cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I/lib/modules/2.6.39-rc6-mmotm0506//build/include -I/lib/modules/2.6.39-rc6-mmotm0506//arch/x86/include/generated -include /lib/modules/2.6.39-rc6-mmotm0506//build/include/generated/autoconf.h -I/lib/modules/2.6.39-rc6-mmotm0506//build/arch/x86/include -I/lib/modules/2.6.39-rc6-mmotm0506//include/generated -Os -c /tmp/kernconf.c
> cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I${kern}/build/include -I$kern/arch/x86/include/generated -include ${kern}/build/include/generated/autoconf.h -I${kern}/build/arch/x86/include -I${kern}/include/generated -c /tmp/kernconf.c
> + cc -D__KERNEL__ -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.6.0/include -I/lib/modules/2.6.39-rc6-mmotm0506//build/include -I/lib/modules/2.6.39-rc6-mmotm0506//arch/x86/include/generated -include /lib/modules/2.6.39-rc6-mmotm0506//build/include/generated/autoconf.h -I/lib/modules/2.6.39-rc6-mmotm0506//build/arch/x86/include -I/lib/modules/2.6.39-rc6-mmotm0506//include/generated -c /tmp/kernconf.c
> In file included from /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/sem.h:81:0,
>                  from /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/sched.h:72,
>                  from /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/utsname.h:35,
>                  from /tmp/kernconf.c:2:
> /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/rcupdate.h: In function '__kfree_rcu':
> /lib/modules/2.6.39-rc6-mmotm0506//build/include/linux/rcupdate.h:822:2: error: size of unnamed array is negative
> 
> rm /tmp/kernconf.c
> + rm /tmp/kernconf.c
> 
> 

We use __always_inline for __Kfree_rcu(), we hope compiler does not compile
it stand-alone, but it seems that __always_inline can't work without optimization,
so you can add "-O2"(kernel build option) or "-Os" option for you third-party kernel
modules' build.

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