[deliverable/linux.git] / arch / s390 / kernel / process.c

/*
 * This file handles the architecture dependent parts of process handling.
 *
 *    Copyright IBM Corp. 1999,2009
 *    Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>,
 *		 Hartmut Penner <hp@de.ibm.com>,
 *		 Denis Joseph Barrow,
 */

#include <linux/compiler.h>
#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/user.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/tick.h>
#include <linux/elfcore.h>
#include <linux/kernel_stat.h>
#include <linux/syscalls.h>
#include <linux/compat.h>
#include <asm/compat.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/processor.h>
#include <asm/irq.h>
#include <asm/timer.h>
#include <asm/nmi.h>
#include "entry.h"

asmlinkage void ret_from_fork(void) asm ("ret_from_fork");

/*
 * Return saved PC of a blocked thread. used in kernel/sched.
 * resume in entry.S does not create a new stack frame, it
 * just stores the registers %r6-%r15 to the frame given by
 * schedule. We want to return the address of the caller of
 * schedule, so we have to walk the backchain one time to
 * find the frame schedule() store its return address.
 */
unsigned long thread_saved_pc(struct task_struct *tsk)
{
	struct stack_frame *sf, *low, *high;

	if (!tsk || !task_stack_page(tsk))
		return 0;
	low = task_stack_page(tsk);
	high = (struct stack_frame *) task_pt_regs(tsk);
	sf = (struct stack_frame *) (tsk->thread.ksp & PSW_ADDR_INSN);
	if (sf <= low || sf > high)
		return 0;
	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
	if (sf <= low || sf > high)
		return 0;
	return sf->gprs[8];
}

/*
 * The idle loop on a S390...
 */
static void default_idle(void)
{
	/* CPU is going idle. */
	local_irq_disable();
	if (need_resched()) {
		local_irq_enable();
		return;
	}
#ifdef CONFIG_HOTPLUG_CPU
	if (cpu_is_offline(smp_processor_id())) {
		preempt_enable_no_resched();
		cpu_die();
	}
#endif
	local_mcck_disable();
	if (test_thread_flag(TIF_MCCK_PENDING)) {
		local_mcck_enable();
		local_irq_enable();
		s390_handle_mcck();
		return;
	}
	trace_hardirqs_on();
	/* Don't trace preempt off for idle. */
	stop_critical_timings();
	/* Stop virtual timer and halt the cpu. */
	vtime_stop_cpu();
	/* Reenable preemption tracer. */
	start_critical_timings();
}

void cpu_idle(void)
{
	for (;;) {
		tick_nohz_stop_sched_tick(1);
		while (!need_resched())
			default_idle();
		tick_nohz_restart_sched_tick();
		preempt_enable_no_resched();
		schedule();
		preempt_disable();
	}
}

extern void kernel_thread_starter(void);

asm(
	".align 4\n"
	"kernel_thread_starter:\n"
	"    la    2,0(10)\n"
	"    basr  14,9\n"
	"    la    2,0\n"
	"    br    11\n");

int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
{
	struct pt_regs regs;

	memset(&regs, 0, sizeof(regs));
	regs.psw.mask = psw_kernel_bits | PSW_MASK_IO | PSW_MASK_EXT;
	regs.psw.addr = (unsigned long) kernel_thread_starter | PSW_ADDR_AMODE;
	regs.gprs[9] = (unsigned long) fn;
	regs.gprs[10] = (unsigned long) arg;
	regs.gprs[11] = (unsigned long) do_exit;
	regs.orig_gpr2 = -1;

	/* Ok, create the new process.. */
	return do_fork(flags | CLONE_VM | CLONE_UNTRACED,
		       0, &regs, 0, NULL, NULL);
}
EXPORT_SYMBOL(kernel_thread);

/*
 * Free current thread data structures etc..
 */
void exit_thread(void)
{
}

void flush_thread(void)
{
	clear_used_math();
	clear_tsk_thread_flag(current, TIF_USEDFPU);
}

void release_thread(struct task_struct *dead_task)
{
}

int copy_thread(unsigned long clone_flags, unsigned long new_stackp,
		unsigned long unused,
		struct task_struct *p, struct pt_regs *regs)
{
	struct thread_info *ti;
	struct fake_frame
	{
		struct stack_frame sf;
		struct pt_regs childregs;
	} *frame;

	frame = container_of(task_pt_regs(p), struct fake_frame, childregs);
	p->thread.ksp = (unsigned long) frame;
	/* Store access registers to kernel stack of new process. */
	frame->childregs = *regs;
	frame->childregs.gprs[2] = 0;	/* child returns 0 on fork. */
	frame->childregs.gprs[15] = new_stackp;
	frame->sf.back_chain = 0;

	/* new return point is ret_from_fork */
	frame->sf.gprs[8] = (unsigned long) ret_from_fork;

	/* fake return stack for resume(), don't go back to schedule */
	frame->sf.gprs[9] = (unsigned long) frame;

	/* Save access registers to new thread structure. */
	save_access_regs(&p->thread.acrs[0]);

#ifndef CONFIG_64BIT
	/*
	 * save fprs to current->thread.fp_regs to merge them with
	 * the emulated registers and then copy the result to the child.
	 */
	save_fp_regs(&current->thread.fp_regs);
	memcpy(&p->thread.fp_regs, &current->thread.fp_regs,
	       sizeof(s390_fp_regs));
	/* Set a new TLS ?  */
	if (clone_flags & CLONE_SETTLS)
		p->thread.acrs[0] = regs->gprs[6];
#else /* CONFIG_64BIT */
	/* Save the fpu registers to new thread structure. */
	save_fp_regs(&p->thread.fp_regs);
	/* Set a new TLS ?  */
	if (clone_flags & CLONE_SETTLS) {
		if (is_compat_task()) {
			p->thread.acrs[0] = (unsigned int) regs->gprs[6];
		} else {
			p->thread.acrs[0] = (unsigned int)(regs->gprs[6] >> 32);
			p->thread.acrs[1] = (unsigned int) regs->gprs[6];
		}
	}
#endif /* CONFIG_64BIT */
	/* start new process with ar4 pointing to the correct address space */
	p->thread.mm_segment = get_fs();
	/* Don't copy debug registers */
	memset(&p->thread.per_info, 0, sizeof(p->thread.per_info));
	/* Initialize per thread user and system timer values */
	ti = task_thread_info(p);
	ti->user_timer = 0;
	ti->system_timer = 0;
	return 0;
}

SYSCALL_DEFINE0(fork)
{
	struct pt_regs *regs = task_pt_regs(current);
	return do_fork(SIGCHLD, regs->gprs[15], regs, 0, NULL, NULL);
}

SYSCALL_DEFINE4(clone, unsigned long, newsp, unsigned long, clone_flags,
		int __user *, parent_tidptr, int __user *, child_tidptr)
{
	struct pt_regs *regs = task_pt_regs(current);

	if (!newsp)
		newsp = regs->gprs[15];
	return do_fork(clone_flags, newsp, regs, 0,
		       parent_tidptr, child_tidptr);
}

/*
 * This is trivial, and on the face of it looks like it
 * could equally well be done in user mode.
 *
 * Not so, for quite unobvious reasons - register pressure.
 * In user mode vfork() cannot have a stack frame, and if
 * done by calling the "clone()" system call directly, you
 * do not have enough call-clobbered registers to hold all
 * the information you need.
 */
SYSCALL_DEFINE0(vfork)
{
	struct pt_regs *regs = task_pt_regs(current);
	return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD,
		       regs->gprs[15], regs, 0, NULL, NULL);
}

asmlinkage void execve_tail(void)
{
	current->thread.fp_regs.fpc = 0;
	if (MACHINE_HAS_IEEE)
		asm volatile("sfpc %0,%0" : : "d" (0));
}

/*
 * sys_execve() executes a new program.
 */
SYSCALL_DEFINE3(execve, char __user *, name, char __user * __user *, argv,
		char __user * __user *, envp)
{
	struct pt_regs *regs = task_pt_regs(current);
	char *filename;
	long rc;

	filename = getname(name);
	rc = PTR_ERR(filename);
	if (IS_ERR(filename))
		return rc;
	rc = do_execve(filename, argv, envp, regs);
	if (rc)
		goto out;
	execve_tail();
	rc = regs->gprs[2];
out:
	putname(filename);
	return rc;
}

/*
 * fill in the FPU structure for a core dump.
 */
int dump_fpu (struct pt_regs * regs, s390_fp_regs *fpregs)
{
#ifndef CONFIG_64BIT
	/*
	 * save fprs to current->thread.fp_regs to merge them with
	 * the emulated registers and then copy the result to the dump.
	 */
	save_fp_regs(&current->thread.fp_regs);
	memcpy(fpregs, &current->thread.fp_regs, sizeof(s390_fp_regs));
#else /* CONFIG_64BIT */
	save_fp_regs(fpregs);
#endif /* CONFIG_64BIT */
	return 1;
}
EXPORT_SYMBOL(dump_fpu);

unsigned long get_wchan(struct task_struct *p)
{
	struct stack_frame *sf, *low, *high;
	unsigned long return_address;
	int count;

	if (!p || p == current || p->state == TASK_RUNNING || !task_stack_page(p))
		return 0;
	low = task_stack_page(p);
	high = (struct stack_frame *) task_pt_regs(p);
	sf = (struct stack_frame *) (p->thread.ksp & PSW_ADDR_INSN);
	if (sf <= low || sf > high)
		return 0;
	for (count = 0; count < 16; count++) {
		sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
		if (sf <= low || sf > high)
			return 0;
		return_address = sf->gprs[8] & PSW_ADDR_INSN;
		if (!in_sched_functions(return_address))
			return return_address;
	}
	return 0;
}
Commit	Line	Data
1da177e4	1	/*
cbdc2292	2	* This file handles the architecture dependent parts of process handling.
1da177e4	3	*
cbdc2292 HC	4	* Copyright IBM Corp. 1999,2009
	5	* Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>,
	6	* Hartmut Penner <hp@de.ibm.com>,
	7	* Denis Joseph Barrow,
1da177e4 LT	8	*/
1da177e4 LT	9
1da177e4 LT	10	#include <linux/compiler.h>
	11	#include <linux/cpu.h>
	12	#include <linux/errno.h>
	13	#include <linux/sched.h>
	14	#include <linux/kernel.h>
	15	#include <linux/mm.h>
4e950f6f	16	#include <linux/fs.h>
1da177e4	17	#include <linux/smp.h>
1da177e4 LT	18	#include <linux/stddef.h>
	19	#include <linux/unistd.h>
	20	#include <linux/ptrace.h>
	21	#include <linux/slab.h>
	22	#include <linux/vmalloc.h>
	23	#include <linux/user.h>
1da177e4 LT	24	#include <linux/interrupt.h>
	25	#include <linux/delay.h>
	26	#include <linux/reboot.h>
	27	#include <linux/init.h>
	28	#include <linux/module.h>
	29	#include <linux/notifier.h>
5a62b192	30	#include <linux/tick.h>
a806170e	31	#include <linux/elfcore.h>
6f430924	32	#include <linux/kernel_stat.h>
26689452	33	#include <linux/syscalls.h>
3e86a8c6	34	#include <linux/compat.h>
7757591a	35	#include <asm/compat.h>
1da177e4 LT	36	#include <asm/uaccess.h>
	37	#include <asm/pgtable.h>
	38	#include <asm/system.h>
	39	#include <asm/io.h>
	40	#include <asm/processor.h>
	41	#include <asm/irq.h>
	42	#include <asm/timer.h>
f5daba1d	43	#include <asm/nmi.h>
a806170e	44	#include "entry.h"
1da177e4	45
94c12cc7	46	asmlinkage void ret_from_fork(void) asm ("ret_from_fork");
1da177e4 LT	47
	48	/*
	49	* Return saved PC of a blocked thread. used in kernel/sched.
	50	* resume in entry.S does not create a new stack frame, it
	51	* just stores the registers %r6-%r15 to the frame given by
	52	* schedule. We want to return the address of the caller of
	53	* schedule, so we have to walk the backchain one time to
	54	* find the frame schedule() store its return address.
	55	*/
	56	unsigned long thread_saved_pc(struct task_struct *tsk)
	57	{
eb33c190	58	struct stack_frame sf, low, *high;
1da177e4	59
eb33c190 HC	60	if (!tsk \|\| !task_stack_page(tsk))
	61	return 0;
	62	low = task_stack_page(tsk);
	63	high = (struct stack_frame *) task_pt_regs(tsk);
	64	sf = (struct stack_frame *) (tsk->thread.ksp & PSW_ADDR_INSN);
	65	if (sf <= low \|\| sf > high)
	66	return 0;
	67	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
	68	if (sf <= low \|\| sf > high)
	69	return 0;
1da177e4 LT	70	return sf->gprs[8];
	71	}
	72
1da177e4 LT	73	/*
	74	* The idle loop on a S390...
	75	*/
cdb04527	76	static void default_idle(void)
1da177e4	77	{
64c7c8f8	78	/* CPU is going idle. */
1da177e4	79	local_irq_disable();
64c7c8f8	80	if (need_resched()) {
1da177e4	81	local_irq_enable();
64c7c8f8 NP	82	return;
64c7c8f8 NP	83	}
1da177e4	84	#ifdef CONFIG_HOTPLUG_CPU
43ca5c3a	85	if (cpu_is_offline(smp_processor_id())) {
1fca251f	86	preempt_enable_no_resched();
1da177e4	87	cpu_die();
1fca251f	88	}
1da177e4	89	#endif
77fa2245 HC	90	local_mcck_disable();
	91	if (test_thread_flag(TIF_MCCK_PENDING)) {
	92	local_mcck_enable();
	93	local_irq_enable();
	94	s390_handle_mcck();
	95	return;
	96	}
1f194a4c	97	trace_hardirqs_on();
632448f6 HC	98	/* Don't trace preempt off for idle. */
632448f6 HC	99	stop_critical_timings();
9cfb9b3c MS	100	/* Stop virtual timer and halt the cpu. */
	101	vtime_stop_cpu();
	102	/* Reenable preemption tracer. */
632448f6	103	start_critical_timings();
1da177e4 LT	104	}
	105
	106	void cpu_idle(void)
	107	{
5bfb5d69	108	for (;;) {
e338125b	109	tick_nohz_stop_sched_tick(1);
5bfb5d69 NP	110	while (!need_resched())
5bfb5d69 NP	111	default_idle();
5a62b192	112	tick_nohz_restart_sched_tick();
5bfb5d69 NP	113	preempt_enable_no_resched();
	114	schedule();
	115	preempt_disable();
	116	}
1da177e4 LT	117	}
1da177e4 LT	118
1da177e4 LT	119	extern void kernel_thread_starter(void);
1da177e4 LT	120
94c12cc7 MS	121	asm(
94c12cc7 MS	122	".align 4\n"
1da177e4 LT	123	"kernel_thread_starter:\n"
	124	" la 2,0(10)\n"
	125	" basr 14,9\n"
	126	" la 2,0\n"
	127	" br 11\n");
	128
	129	int kernel_thread(int (fn)(void ), void * arg, unsigned long flags)
	130	{
	131	struct pt_regs regs;
	132
	133	memset(&regs, 0, sizeof(regs));
c1821c2e	134	regs.psw.mask = psw_kernel_bits \| PSW_MASK_IO \| PSW_MASK_EXT;
1da177e4 LT	135	regs.psw.addr = (unsigned long) kernel_thread_starter \| PSW_ADDR_AMODE;
	136	regs.gprs[9] = (unsigned long) fn;
	137	regs.gprs[10] = (unsigned long) arg;
	138	regs.gprs[11] = (unsigned long) do_exit;
	139	regs.orig_gpr2 = -1;
	140
	141	/* Ok, create the new process.. */
	142	return do_fork(flags \| CLONE_VM \| CLONE_UNTRACED,
	143	0, &regs, 0, NULL, NULL);
	144	}
1485c5c8	145	EXPORT_SYMBOL(kernel_thread);
1da177e4 LT	146
	147	/*
	148	* Free current thread data structures etc..
	149	*/
	150	void exit_thread(void)
	151	{
	152	}
	153
	154	void flush_thread(void)
	155	{
	156	clear_used_math();
	157	clear_tsk_thread_flag(current, TIF_USEDFPU);
	158	}
	159
	160	void release_thread(struct task_struct *dead_task)
	161	{
	162	}
	163
6f2c55b8	164	int copy_thread(unsigned long clone_flags, unsigned long new_stackp,
cbdc2292 HC	165	unsigned long unused,
cbdc2292 HC	166	struct task_struct p, struct pt_regs regs)
1da177e4	167	{
5168ce2c	168	struct thread_info *ti;
cbdc2292 HC	169	struct fake_frame
	170	{
	171	struct stack_frame sf;
	172	struct pt_regs childregs;
	173	} *frame;
	174
	175	frame = container_of(task_pt_regs(p), struct fake_frame, childregs);
	176	p->thread.ksp = (unsigned long) frame;
1da177e4	177	/* Store access registers to kernel stack of new process. */
cbdc2292	178	frame->childregs = *regs;
1da177e4	179	frame->childregs.gprs[2] = 0; /* child returns 0 on fork. */
cbdc2292 HC	180	frame->childregs.gprs[15] = new_stackp;
cbdc2292 HC	181	frame->sf.back_chain = 0;
1da177e4	182
cbdc2292 HC	183	/* new return point is ret_from_fork */
cbdc2292 HC	184	frame->sf.gprs[8] = (unsigned long) ret_from_fork;
1da177e4	185
cbdc2292 HC	186	/* fake return stack for resume(), don't go back to schedule */
cbdc2292 HC	187	frame->sf.gprs[9] = (unsigned long) frame;
1da177e4 LT	188
	189	/* Save access registers to new thread structure. */
	190	save_access_regs(&p->thread.acrs[0]);
	191
347a8dc3	192	#ifndef CONFIG_64BIT
cbdc2292	193	/*
1da177e4 LT	194	* save fprs to current->thread.fp_regs to merge them with
	195	* the emulated registers and then copy the result to the child.
	196	*/
	197	save_fp_regs(&current->thread.fp_regs);
	198	memcpy(&p->thread.fp_regs, &current->thread.fp_regs,
	199	sizeof(s390_fp_regs));
1da177e4 LT	200	/* Set a new TLS ? */
	201	if (clone_flags & CLONE_SETTLS)
	202	p->thread.acrs[0] = regs->gprs[6];
347a8dc3	203	#else /* CONFIG_64BIT */
1da177e4 LT	204	/* Save the fpu registers to new thread structure. */
1da177e4 LT	205	save_fp_regs(&p->thread.fp_regs);
1da177e4 LT	206	/* Set a new TLS ? */
1da177e4 LT	207	if (clone_flags & CLONE_SETTLS) {
7757591a	208	if (is_compat_task()) {
1da177e4 LT	209	p->thread.acrs[0] = (unsigned int) regs->gprs[6];
	210	} else {
	211	p->thread.acrs[0] = (unsigned int)(regs->gprs[6] >> 32);
	212	p->thread.acrs[1] = (unsigned int) regs->gprs[6];
	213	}
	214	}
347a8dc3	215	#endif /* CONFIG_64BIT */
1da177e4 LT	216	/* start new process with ar4 pointing to the correct address space */
1da177e4 LT	217	p->thread.mm_segment = get_fs();
cbdc2292 HC	218	/* Don't copy debug registers */
cbdc2292 HC	219	memset(&p->thread.per_info, 0, sizeof(p->thread.per_info));
5168ce2c HC	220	/* Initialize per thread user and system timer values */
	221	ti = task_thread_info(p);
	222	ti->user_timer = 0;
	223	ti->system_timer = 0;
cbdc2292	224	return 0;
1da177e4 LT	225	}
1da177e4 LT	226
26689452	227	SYSCALL_DEFINE0(fork)
1da177e4	228	{
03ff9a23 MS	229	struct pt_regs *regs = task_pt_regs(current);
03ff9a23 MS	230	return do_fork(SIGCHLD, regs->gprs[15], regs, 0, NULL, NULL);
1da177e4 LT	231	}
1da177e4 LT	232
2d70ca23 HC	233	SYSCALL_DEFINE4(clone, unsigned long, newsp, unsigned long, clone_flags,
2d70ca23 HC	234	int __user , parent_tidptr, int __user , child_tidptr)
1da177e4	235	{
03ff9a23	236	struct pt_regs *regs = task_pt_regs(current);
1da177e4	237
03ff9a23 MS	238	if (!newsp)
	239	newsp = regs->gprs[15];
	240	return do_fork(clone_flags, newsp, regs, 0,
1da177e4 LT	241	parent_tidptr, child_tidptr);
	242	}
	243
	244	/*
	245	* This is trivial, and on the face of it looks like it
	246	* could equally well be done in user mode.
	247	*
	248	* Not so, for quite unobvious reasons - register pressure.
	249	* In user mode vfork() cannot have a stack frame, and if
	250	* done by calling the "clone()" system call directly, you
	251	* do not have enough call-clobbered registers to hold all
	252	* the information you need.
	253	*/
26689452	254	SYSCALL_DEFINE0(vfork)
1da177e4	255	{
03ff9a23	256	struct pt_regs *regs = task_pt_regs(current);
1da177e4	257	return do_fork(CLONE_VFORK \| CLONE_VM \| SIGCHLD,
03ff9a23 MS	258	regs->gprs[15], regs, 0, NULL, NULL);
	259	}
	260
	261	asmlinkage void execve_tail(void)
	262	{
03ff9a23 MS	263	current->thread.fp_regs.fpc = 0;
	264	if (MACHINE_HAS_IEEE)
	265	asm volatile("sfpc %0,%0" : : "d" (0));
1da177e4 LT	266	}
	267
	268	/*
	269	* sys_execve() executes a new program.
	270	*/
3e86a8c6 HC	271	SYSCALL_DEFINE3(execve, char __user , name, char __user __user *, argv,
3e86a8c6 HC	272	char __user * __user *, envp)
1da177e4	273	{
03ff9a23 MS	274	struct pt_regs *regs = task_pt_regs(current);
03ff9a23 MS	275	char *filename;
3e86a8c6	276	long rc;
03ff9a23	277
3e86a8c6 HC	278	filename = getname(name);
	279	rc = PTR_ERR(filename);
	280	if (IS_ERR(filename))
	281	return rc;
	282	rc = do_execve(filename, argv, envp, regs);
	283	if (rc)
03ff9a23	284	goto out;
03ff9a23	285	execve_tail();
3e86a8c6	286	rc = regs->gprs[2];
1da177e4	287	out:
3e86a8c6 HC	288	putname(filename);
3e86a8c6 HC	289	return rc;
1da177e4 LT	290	}
1da177e4 LT	291
1da177e4 LT	292	/*
	293	* fill in the FPU structure for a core dump.
	294	*/
	295	int dump_fpu (struct pt_regs * regs, s390_fp_regs *fpregs)
	296	{
347a8dc3	297	#ifndef CONFIG_64BIT
cbdc2292	298	/*
1da177e4 LT	299	* save fprs to current->thread.fp_regs to merge them with
	300	* the emulated registers and then copy the result to the dump.
	301	*/
	302	save_fp_regs(&current->thread.fp_regs);
	303	memcpy(fpregs, &current->thread.fp_regs, sizeof(s390_fp_regs));
347a8dc3	304	#else /* CONFIG_64BIT */
1da177e4	305	save_fp_regs(fpregs);
347a8dc3	306	#endif /* CONFIG_64BIT */
1da177e4 LT	307	return 1;
1da177e4 LT	308	}
1485c5c8	309	EXPORT_SYMBOL(dump_fpu);
1da177e4	310
1da177e4 LT	311	unsigned long get_wchan(struct task_struct *p)
	312	{
	313	struct stack_frame sf, low, *high;
	314	unsigned long return_address;
	315	int count;
	316
30af7120	317	if (!p \|\| p == current \|\| p->state == TASK_RUNNING \|\| !task_stack_page(p))
1da177e4	318	return 0;
30af7120 AV	319	low = task_stack_page(p);
30af7120 AV	320	high = (struct stack_frame *) task_pt_regs(p);
1da177e4 LT	321	sf = (struct stack_frame *) (p->thread.ksp & PSW_ADDR_INSN);
	322	if (sf <= low \|\| sf > high)
	323	return 0;
	324	for (count = 0; count < 16; count++) {
	325	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
	326	if (sf <= low \|\| sf > high)
	327	return 0;
	328	return_address = sf->gprs[8] & PSW_ADDR_INSN;
	329	if (!in_sched_functions(return_address))
	330	return return_address;
	331	}
	332	return 0;
	333	}