linux-kernel - Re: KPROBE linking error (who's the maintainer of kernel/power/) ?

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Date:	Mon, 5 Jan 2009 14:16:03 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Cheng Renquan (程任全)" 
	<crquan@...il.com>
Cc:	"Arjan van de Ven" <arjan@...ux.intel.com>,
	"Al Viro" <viro@...iv.linux.org.uk>,
	"Matt Helsley" <matthltc@...ibm.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Adrian Bunk" <bunk@...nel.org>,
	"Ananth N Mavinakayanahalli" <ananth@...ibm.com>,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	mhiramat@...hat.com, linux-kernel@...r.kernel.org,
	Pavel Machek <pavel@...e.cz>
Subject: Re: KPROBE linking error (who's the maintainer of kernel/power/) ?

Hi,

On Monday 05 January 2009, Cheng Renquan (程任全) wrote:
> with this .config
> 
> CONFIG_CGROUPS=y
> CONFIG_CGROUP_FREEZER=y
> CONFIG_MODULES=y
> CONFIG_FREEZER=y
> CONFIG_PM=y
> CONFIG_PM_SLEEP=n
> 
> the kernel will end compiling with error:
> 
> kernel/built-in.o: In function `check_safety':
> /usr/src/linux-2.6.28/kernel/kprobes.c:126: undefined reference to
> `freeze_processes'
> /usr/src/linux-2.6.28/kernel/kprobes.c:139: undefined reference to
> `thaw_processes'
> /usr/src/linux-2.6.28/kernel/kprobes.c:139: undefined reference to
> `thaw_processes'
> make: *** [.tmp_vmlinux1] Error 1

So there is a bug, thanks for the report.

> By read kernel/kprobes.c, I found there maybe a bug:
> 
> 1. "check_safety" in "kernel/kprobes.c" call thaw_processes if both
> CONFIG_PREEMPT and CONFIG_PM defined,
> 2. "thaw_processes" function is implemented in "kernel/power/process.c",
> 3. but it is only used if CONFIG_FREEZER defined, from <linux/freezer.h>,
> 4. else (CONFIG_FREEZER undefined) it's a null macro defined in
> <linux/freezer.h>,
> 5. but process.o only get compile if CONFIG_PM_SLEEP defined, from
> "kernel/power/Makefile",
> 
> Now I'm confused on how to resolve this?

I'd make process.o depend on CONFIG_FREEZER (patch below).

> What's the relation of PM, PM_SLEEP, and FREEZER?

PM_SLEEP depends on PM and FREEZER is defined in kernel/Kconfig.freezer as

config FREEZER
        def_bool PM_SLEEP || CGROUP_FREEZER

> Which modification of the following will be better?
> 1. modify kernel/Kconfig, let KPROBES depends more?
> 2. modify kernel/kprobes.c, let the conditional compile depends more?
> 3. modify include/linux/freezer.h, move thaw_processes to include/linux/pm.h?
> 4. modify kernel/power/Makefile, let kernel/power/process.c compile on
> less condition?
> 
> Furthermore, there seems no entry for maintainers of "kernel/power/",
> who maintain that subdir please add your name to the MAINTAINERS file?
> I just grab some latest touchers of kernel/power/ and kernel/kprobes.c
> as the recipients here.

I'm one of the maintainers.

Thanks,
Rafael

---
Subject: PM: Fix freezer compilation if PM_SLEEP is unset
From: Rafael J. Wysocki <rjw@...k.pl>

Freezer fails to compile if with the following configuration
settings:

CONFIG_CGROUPS=y
CONFIG_CGROUP_FREEZER=y
CONFIG_MODULES=y
CONFIG_FREEZER=y
CONFIG_PM=y
CONFIG_PM_SLEEP=n

Fix this by making process.o compilation depend on CONFIG_FREEZER.

Reported-by: Cheng Renquan <crquan@...il.com>
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 kernel/power/Makefile |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/power/Makefile
===================================================================
--- linux-2.6.orig/kernel/power/Makefile
+++ linux-2.6/kernel/power/Makefile
@@ -4,7 +4,8 @@ EXTRA_CFLAGS	+=	-DDEBUG
 endif
 
 obj-y				:= main.o
-obj-$(CONFIG_PM_SLEEP)		+= process.o console.o
+obj-$(CONFIG_PM_SLEEP)		+= console.o
+obj-$(CONFIG_FREEZER)		+= process.o
 obj-$(CONFIG_HIBERNATION)	+= swsusp.o disk.o snapshot.o swap.o user.o
 
 obj-$(CONFIG_MAGIC_SYSRQ)	+= poweroff.o


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