[ARM] Tidy up context switch save area initialisation for fork

Fix a minor bug where we jump to ret_from_fork with IRQs enabled.

arch/arm/kernel/process.c

@@ -310,9 +310,9 @@ void release_thread(struct task_struct *dead_task)
 
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
 
-int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
-	unsigned long unused,
-	struct task_struct * p, struct pt_regs * regs)
+int
+copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
+	    unsigned long unused, struct task_struct *p, struct pt_regs *regs)
 {
 	struct pt_regs *childregs;
 	struct cpu_context_save *save;
@@ -323,8 +323,8 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
 	childregs->ARM_sp = esp;
 
 	save = ((struct cpu_context_save *)(childregs)) - 1;
-	*save = INIT_CSS;
-	save->pc |= (unsigned long)ret_from_fork;
+	memset(save, 0, sizeof(struct cpu_context_save));
+	init_pc_psr(save, ret_from_fork);
 
 	p->thread_info->cpu_context = save;
 

include/asm-arm/proc-armo/processor.h

@@ -20,6 +20,7 @@
 #define __ASM_PROC_PROCESSOR_H
 
 #include <linux/string.h>
+#include <asm/proc/ptrace.h>
 
 #define KERNEL_STACK_SIZE 4096
 
@@ -35,7 +36,10 @@ struct cpu_context_save {
 	unsigned long pc;
 };
 
-#define INIT_CSS (struct cpu_context_save){ 0, 0, 0, 0, 0, 0, 0, 0, SVC26_MODE }
+static inline void init_pc_psr(struct cpu_context_save *s, void *fn)
+{
+	s->pc = ((unsigned long)fn) | PSR_I_BIT | SVC26_MODE;
+}
 
 typedef struct {
 	void (*put_byte)(void);			/* Special calling convention */

include/asm-arm/proc-armv/processor.h

@@ -19,6 +19,7 @@
 #define __ASM_PROC_PROCESSOR_H
 
 #include <asm/proc/domain.h>
+#include <asm/proc/ptrace.h>
 
 #define KERNEL_STACK_SIZE	PAGE_SIZE
 
@@ -35,7 +36,11 @@ struct cpu_context_save {
 	unsigned long pc;
 };
 
-#define INIT_CSS (struct cpu_context_save){ SVC_MODE, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
+static inline void init_pc_psr(struct cpu_context_save *s, void *fn)
+{
+	s->pc = (unsigned long)fn;
+	s->cpsr = PSR_I_BIT | SVC_MODE;
+}
 
 #define INIT_EXTRA_THREAD_INFO						\
 	cpu_domain:	  domain_val(DOMAIN_USER, DOMAIN_CLIENT) |	\