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Subject[tip:core/locking] locking, m68k: Calculate thread_info offset with asm offset
Commit-ID:  0ee000e5e8fa2e5c760250be0d78d5906e3eb94b
Author: Heiko Carstens <>
AuthorDate: Mon, 31 Aug 2009 14:43:35 +0200
Committer: Ingo Molnar <>
CommitDate: Mon, 31 Aug 2009 18:08:49 +0200

locking, m68k: Calculate thread_info offset with asm offset

m68k has the thread_info structure embedded in its task struct.
Therefore its not possible to implement current_thread_info()
by looking at the stack pointer and do some simple calculations
like most other architectures do it.

To return the thread_info pointer for a task two defines are
used. This works until the spinlock function bodies get moved
into an own header file and CONFIG_SPINLOCK_DEBUG is turned on.
That results into this compile error:

In file included from include/linux/spinlock.h:378,
from include/linux/seqlock.h:29,
from include/linux/time.h:8,
from include/linux/timex.h:56,
from include/linux/sched.h:54,
from arch/m68k/kernel/asm-offsets.c:12:
include/linux/spinlock_api_smp.h: In function '__spin_unlock_irq':
include/linux/spinlock_api_smp.h:371: error: 'current' undeclared (first use in this function)
include/linux/spinlock_api_smp.h:371: error: (Each undeclared identifier is reported only once
include/linux/spinlock_api_smp.h:371: error: for each function it appears in.)

Including asm/current.h to asm-offsets.c wouldn't help since
the definition of struct task is needed. So we end up with ugly
header file include dependencies.

To solve this calculate the offset of the thread_info structure
into the task struct in asm-offsets.h and use the offset in
task_thread_info(). This works just like it does for IA64 as

Signed-off-by: Heiko Carstens <>
Acked-by: Peter Zijlstra <>
Cc: Arnd Bergmann <>
Cc: Nick Piggin <>
Cc: Martin Schwidefsky <>
Cc: Horst Hartmann <>
Cc: Christian Ehrhardt <>
Cc: Andrew Morton <>
Cc: Linus Torvalds <>
Cc: David Miller <>
Cc: Benjamin Herrenschmidt <>
Cc: Paul Mackerras <>
Cc: Geert Uytterhoeven <>
Cc: Roman Zippel <>
Cc: <>
LKML-Reference: <>
Signed-off-by: Ingo Molnar <>

arch/m68k/include/asm/thread_info_mm.h | 11 ++++++++++-
arch/m68k/kernel/asm-offsets.c | 5 +++++
2 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/arch/m68k/include/asm/thread_info_mm.h b/arch/m68k/include/asm/thread_info_mm.h
index 6ea5c33..b6da388 100644
--- a/arch/m68k/include/asm/thread_info_mm.h
+++ b/arch/m68k/include/asm/thread_info_mm.h
@@ -1,6 +1,10 @@

+#ifndef ASM_OFFSETS_C
+#include <asm/asm-offsets.h>
+#include <asm/current.h>
#include <asm/types.h>
#include <asm/page.h>

@@ -31,7 +35,12 @@ struct thread_info {
#define init_thread_info (
#define init_stack (init_thread_union.stack)

-#define task_thread_info(tsk) (&(tsk)->
+#define task_thread_info(tsk) ((struct thread_info *) NULL)
+#define task_thread_info(tsk) ((struct thread_info *)((char *)tsk+TASK_TINFO))
#define task_stack_page(tsk) ((tsk)->stack)
#define current_thread_info() task_thread_info(current)

diff --git a/arch/m68k/kernel/asm-offsets.c b/arch/m68k/kernel/asm-offsets.c
index 0cffab8..25d6b72 100644
--- a/arch/m68k/kernel/asm-offsets.c
+++ b/arch/m68k/kernel/asm-offsets.c
@@ -8,6 +8,8 @@
* #defines from the assembly-language output.

+#define ASM_OFFSETS_C
#include <linux/stddef.h>
#include <linux/sched.h>
#include <linux/kernel_stat.h>
@@ -27,6 +29,9 @@ int main(void)
DEFINE(TASK_INFO, offsetof(struct task_struct,;
DEFINE(TASK_MM, offsetof(struct task_struct, mm));
DEFINE(TASK_ACTIVE_MM, offsetof(struct task_struct, active_mm));
+#ifdef CONFIG_MMU
+ DEFINE(TASK_TINFO, offsetof(struct task_struct,;

/* offsets into the thread struct */
DEFINE(THREAD_KSP, offsetof(struct thread_struct, ksp));

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