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
well.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Horst Hartmann <horsth@linux.vnet.ibm.com>
Cc: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Miller <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: <linux-arch@vger.kernel.org>
LKML-Reference: <20090831124417.329662275@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/m68k/include/asm/thread_info_mm.h

 #ifndef _ASM_M68K_THREAD_INFO_H
 #define _ASM_M68K_THREAD_INFO_H
 
+#ifndef ASM_OFFSETS_C
+#include <asm/asm-offsets.h>
+#endif
+#include <asm/current.h>
 #include <asm/types.h>
 #include <asm/page.h>
 
@@ -31,7 +35,12 @@ struct thread_info {
 #define init_thread_info	(init_task.thread.info)
 #define init_stack		(init_thread_union.stack)
 
-#define task_thread_info(tsk)	(&(tsk)->thread.info)
+#ifdef ASM_OFFSETS_C
+#define task_thread_info(tsk)	((struct thread_info *) NULL)
+#else
+#define task_thread_info(tsk)	((struct thread_info *)((char *)tsk+TASK_TINFO))
+#endif
+
 #define task_stack_page(tsk)	((tsk)->stack)
 #define current_thread_info()	task_thread_info(current)
 

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, thread.info));
 	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, thread.info));
+#endif
 
 	/* offsets into the thread struct */
 	DEFINE(THREAD_KSP, offsetof(struct thread_struct, ksp));