linux/arch/alpha/kernel/process.c
Josh Poimboeuf 071c44e427 sched/idle: Mark arch_cpu_idle_dead() __noreturn
Before commit 076cbf5d2163 ("x86/xen: don't let xen_pv_play_dead()
return"), in Xen, when a previously offlined CPU was brought back
online, it unexpectedly resumed execution where it left off in the
middle of the idle loop.

There were some hacks to make that work, but the behavior was surprising
as do_idle() doesn't expect an offlined CPU to return from the dead (in
arch_cpu_idle_dead()).

Now that Xen has been fixed, and the arch-specific implementations of
arch_cpu_idle_dead() also don't return, give it a __noreturn attribute.

This will cause the compiler to complain if an arch-specific
implementation might return.  It also improves code generation for both
caller and callee.

Also fixes the following warning:

  vmlinux.o: warning: objtool: do_idle+0x25f: unreachable instruction

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/60d527353da8c99d4cf13b6473131d46719ed16d.1676358308.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
2023-03-08 08:44:28 -08:00

397 lines
9.8 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* linux/arch/alpha/kernel/process.c
*
* Copyright (C) 1995 Linus Torvalds
*/
/*
* This file handles the architecture-dependent parts of process handling.
*/
#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/ptrace.h>
#include <linux/user.h>
#include <linux/time.h>
#include <linux/major.h>
#include <linux/stat.h>
#include <linux/vt.h>
#include <linux/mman.h>
#include <linux/elfcore.h>
#include <linux/reboot.h>
#include <linux/tty.h>
#include <linux/console.h>
#include <linux/slab.h>
#include <linux/rcupdate.h>
#include <asm/reg.h>
#include <linux/uaccess.h>
#include <asm/io.h>
#include <asm/hwrpb.h>
#include <asm/fpu.h>
#include "proto.h"
#include "pci_impl.h"
/*
* Power off function, if any
*/
void (*pm_power_off)(void) = machine_power_off;
EXPORT_SYMBOL(pm_power_off);
#ifdef CONFIG_ALPHA_WTINT
/*
* Sleep the CPU.
* EV6, LCA45 and QEMU know how to power down, skipping N timer interrupts.
*/
void arch_cpu_idle(void)
{
wtint(0);
}
void __noreturn arch_cpu_idle_dead(void)
{
wtint(INT_MAX);
BUG();
}
#endif /* ALPHA_WTINT */
struct halt_info {
int mode;
char *restart_cmd;
};
static void
common_shutdown_1(void *generic_ptr)
{
struct halt_info *how = generic_ptr;
struct percpu_struct *cpup;
unsigned long *pflags, flags;
int cpuid = smp_processor_id();
/* No point in taking interrupts anymore. */
local_irq_disable();
cpup = (struct percpu_struct *)
((unsigned long)hwrpb + hwrpb->processor_offset
+ hwrpb->processor_size * cpuid);
pflags = &cpup->flags;
flags = *pflags;
/* Clear reason to "default"; clear "bootstrap in progress". */
flags &= ~0x00ff0001UL;
#ifdef CONFIG_SMP
/* Secondaries halt here. */
if (cpuid != boot_cpuid) {
flags |= 0x00040000UL; /* "remain halted" */
*pflags = flags;
set_cpu_present(cpuid, false);
set_cpu_possible(cpuid, false);
halt();
}
#endif
if (how->mode == LINUX_REBOOT_CMD_RESTART) {
if (!how->restart_cmd) {
flags |= 0x00020000UL; /* "cold bootstrap" */
} else {
/* For SRM, we could probably set environment
variables to get this to work. We'd have to
delay this until after srm_paging_stop unless
we ever got srm_fixup working.
At the moment, SRM will use the last boot device,
but the file and flags will be the defaults, when
doing a "warm" bootstrap. */
flags |= 0x00030000UL; /* "warm bootstrap" */
}
} else {
flags |= 0x00040000UL; /* "remain halted" */
}
*pflags = flags;
#ifdef CONFIG_SMP
/* Wait for the secondaries to halt. */
set_cpu_present(boot_cpuid, false);
set_cpu_possible(boot_cpuid, false);
while (!cpumask_empty(cpu_present_mask))
barrier();
#endif
/* If booted from SRM, reset some of the original environment. */
if (alpha_using_srm) {
#ifdef CONFIG_DUMMY_CONSOLE
/* If we've gotten here after SysRq-b, leave interrupt
context before taking over the console. */
if (in_hardirq())
irq_exit();
/* This has the effect of resetting the VGA video origin. */
console_lock();
do_take_over_console(&dummy_con, 0, MAX_NR_CONSOLES-1, 1);
console_unlock();
#endif
pci_restore_srm_config();
set_hae(srm_hae);
}
if (alpha_mv.kill_arch)
alpha_mv.kill_arch(how->mode);
if (! alpha_using_srm && how->mode != LINUX_REBOOT_CMD_RESTART) {
/* Unfortunately, since MILO doesn't currently understand
the hwrpb bits above, we can't reliably halt the
processor and keep it halted. So just loop. */
return;
}
if (alpha_using_srm)
srm_paging_stop();
halt();
}
static void
common_shutdown(int mode, char *restart_cmd)
{
struct halt_info args;
args.mode = mode;
args.restart_cmd = restart_cmd;
on_each_cpu(common_shutdown_1, &args, 0);
}
void
machine_restart(char *restart_cmd)
{
common_shutdown(LINUX_REBOOT_CMD_RESTART, restart_cmd);
}
void
machine_halt(void)
{
common_shutdown(LINUX_REBOOT_CMD_HALT, NULL);
}
void
machine_power_off(void)
{
common_shutdown(LINUX_REBOOT_CMD_POWER_OFF, NULL);
}
/* Used by sysrq-p, among others. I don't believe r9-r15 are ever
saved in the context it's used. */
void
show_regs(struct pt_regs *regs)
{
show_regs_print_info(KERN_DEFAULT);
dik_show_regs(regs, NULL);
}
/*
* Re-start a thread when doing execve()
*/
void
start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
{
regs->pc = pc;
regs->ps = 8;
wrusp(sp);
}
EXPORT_SYMBOL(start_thread);
void
flush_thread(void)
{
/* Arrange for each exec'ed process to start off with a clean slate
with respect to the FPU. This is all exceptions disabled. */
current_thread_info()->ieee_state = 0;
wrfpcr(FPCR_DYN_NORMAL | ieee_swcr_to_fpcr(0));
/* Clean slate for TLS. */
current_thread_info()->pcb.unique = 0;
}
/*
* Copy architecture-specific thread state
*/
int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
{
unsigned long clone_flags = args->flags;
unsigned long usp = args->stack;
unsigned long tls = args->tls;
extern void ret_from_fork(void);
extern void ret_from_kernel_thread(void);
struct thread_info *childti = task_thread_info(p);
struct pt_regs *childregs = task_pt_regs(p);
struct pt_regs *regs = current_pt_regs();
struct switch_stack *childstack, *stack;
childstack = ((struct switch_stack *) childregs) - 1;
childti->pcb.ksp = (unsigned long) childstack;
childti->pcb.flags = 1; /* set FEN, clear everything else */
childti->status |= TS_SAVED_FP | TS_RESTORE_FP;
if (unlikely(args->fn)) {
/* kernel thread */
memset(childstack, 0,
sizeof(struct switch_stack) + sizeof(struct pt_regs));
childstack->r26 = (unsigned long) ret_from_kernel_thread;
childstack->r9 = (unsigned long) args->fn;
childstack->r10 = (unsigned long) args->fn_arg;
childregs->hae = alpha_mv.hae_cache;
memset(childti->fp, '\0', sizeof(childti->fp));
childti->pcb.usp = 0;
return 0;
}
/* Note: if CLONE_SETTLS is not set, then we must inherit the
value from the parent, which will have been set by the block
copy in dup_task_struct. This is non-intuitive, but is
required for proper operation in the case of a threaded
application calling fork. */
if (clone_flags & CLONE_SETTLS)
childti->pcb.unique = tls;
else
regs->r20 = 0; /* OSF/1 has some strange fork() semantics. */
childti->pcb.usp = usp ?: rdusp();
*childregs = *regs;
childregs->r0 = 0;
childregs->r19 = 0;
childregs->r20 = 1; /* OSF/1 has some strange fork() semantics. */
stack = ((struct switch_stack *) regs) - 1;
*childstack = *stack;
childstack->r26 = (unsigned long) ret_from_fork;
return 0;
}
/*
* Fill in the user structure for a ELF core dump.
*/
void
dump_elf_thread(elf_greg_t *dest, struct pt_regs *pt, struct thread_info *ti)
{
/* switch stack follows right below pt_regs: */
struct switch_stack * sw = ((struct switch_stack *) pt) - 1;
dest[ 0] = pt->r0;
dest[ 1] = pt->r1;
dest[ 2] = pt->r2;
dest[ 3] = pt->r3;
dest[ 4] = pt->r4;
dest[ 5] = pt->r5;
dest[ 6] = pt->r6;
dest[ 7] = pt->r7;
dest[ 8] = pt->r8;
dest[ 9] = sw->r9;
dest[10] = sw->r10;
dest[11] = sw->r11;
dest[12] = sw->r12;
dest[13] = sw->r13;
dest[14] = sw->r14;
dest[15] = sw->r15;
dest[16] = pt->r16;
dest[17] = pt->r17;
dest[18] = pt->r18;
dest[19] = pt->r19;
dest[20] = pt->r20;
dest[21] = pt->r21;
dest[22] = pt->r22;
dest[23] = pt->r23;
dest[24] = pt->r24;
dest[25] = pt->r25;
dest[26] = pt->r26;
dest[27] = pt->r27;
dest[28] = pt->r28;
dest[29] = pt->gp;
dest[30] = ti == current_thread_info() ? rdusp() : ti->pcb.usp;
dest[31] = pt->pc;
/* Once upon a time this was the PS value. Which is stupid
since that is always 8 for usermode. Usurped for the more
useful value of the thread's UNIQUE field. */
dest[32] = ti->pcb.unique;
}
EXPORT_SYMBOL(dump_elf_thread);
int
dump_elf_task(elf_greg_t *dest, struct task_struct *task)
{
dump_elf_thread(dest, task_pt_regs(task), task_thread_info(task));
return 1;
}
EXPORT_SYMBOL(dump_elf_task);
int elf_core_copy_task_fpregs(struct task_struct *t, elf_fpregset_t *fpu)
{
memcpy(fpu, task_thread_info(t)->fp, 32 * 8);
return 1;
}
/*
* Return saved PC of a blocked thread. This assumes the frame
* pointer is the 6th saved long on the kernel stack and that the
* saved return address is the first long in the frame. This all
* holds provided the thread blocked through a call to schedule() ($15
* is the frame pointer in schedule() and $15 is saved at offset 48 by
* entry.S:do_switch_stack).
*
* Under heavy swap load I've seen this lose in an ugly way. So do
* some extra sanity checking on the ranges we expect these pointers
* to be in so that we can fail gracefully. This is just for ps after
* all. -- r~
*/
static unsigned long
thread_saved_pc(struct task_struct *t)
{
unsigned long base = (unsigned long)task_stack_page(t);
unsigned long fp, sp = task_thread_info(t)->pcb.ksp;
if (sp > base && sp+6*8 < base + 16*1024) {
fp = ((unsigned long*)sp)[6];
if (fp > sp && fp < base + 16*1024)
return *(unsigned long *)fp;
}
return 0;
}
unsigned long
__get_wchan(struct task_struct *p)
{
unsigned long schedule_frame;
unsigned long pc;
/*
* This one depends on the frame size of schedule(). Do a
* "disass schedule" in gdb to find the frame size. Also, the
* code assumes that sleep_on() follows immediately after
* interruptible_sleep_on() and that add_timer() follows
* immediately after interruptible_sleep(). Ugly, isn't it?
* Maybe adding a wchan field to task_struct would be better,
* after all...
*/
pc = thread_saved_pc(p);
if (in_sched_functions(pc)) {
schedule_frame = ((unsigned long *)task_thread_info(p)->pcb.ksp)[6];
return ((unsigned long *)schedule_frame)[12];
}
return pc;
}