text: /*
   *  linux/kernel/panic.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   */
  
  /*
   * This function is used through-out the kernel (including mm and fs)
   * to indicate a major problem.
   */
  #include <linux/debug_locks.h>
  #include <linux/interrupt.h>
  #include <linux/kmsg_dump.h>
  #include <linux/kallsyms.h>
  #include <linux/notifier.h>
  #include <linux/module.h>
  #include <linux/random.h>
  #include <linux/ftrace.h>
  #include <linux/reboot.h>
  #include <linux/delay.h>
  #include <linux/kexec.h>
  #include <linux/sched.h>
  #include <linux/sysrq.h>
  #include <linux/init.h>
  #include <linux/nmi.h>
  #include <linux/console.h>
  
  #define PANIC_TIMER_STEP 100
  #define PANIC_BLINK_SPD 18
  
  int panic_on_oops = CONFIG_PANIC_ON_OOPS_VALUE;
  static unsigned long tainted_mask;
  static int pause_on_oops;
  static int pause_on_oops_flag;
  static DEFINE_SPINLOCK(pause_on_oops_lock);
  bool crash_kexec_post_notifiers;
  int panic_on_warn __read_mostly;
  
  int panic_timeout = CONFIG_PANIC_TIMEOUT;
  EXPORT_SYMBOL_GPL(panic_timeout);
  
  ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
  
  EXPORT_SYMBOL(panic_notifier_list);
  
  static long no_blink(int state)
  {
  	return 0;
  }
  
  /* Returns how long it waited in ms */
  long (*panic_blink)(int state);
  EXPORT_SYMBOL(panic_blink);
  
  /*
   * Stop ourself in panic -- architecture code may override this
   */
  void __weak panic_smp_self_stop(void)
  {
  	while (1)
  		cpu_relax();
  }
  
  /*
   * Stop ourselves in NMI context if another CPU has already panicked. Arch code
   * may override this to prepare for crash dumping, e.g. save regs info.
   */
  void __weak nmi_panic_self_stop(struct pt_regs *regs)
  {
  	panic_smp_self_stop();
  }
  
  atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
  
  /*
   * A variant of panic() called from NMI context. We return if we've already
   * panicked on this CPU. If another CPU already panicked, loop in
   * nmi_panic_self_stop() which can provide architecture dependent code such
   * as saving register state for crash dump.
   */
  void nmi_panic(struct pt_regs *regs, const char *msg)
  {
  	int old_cpu, cpu;
  
  	cpu = raw_smp_processor_id();
  	old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu);
  
  	if (old_cpu == PANIC_CPU_INVALID)
  		panic("%s", msg);
  	else if (old_cpu != cpu)
  		nmi_panic_self_stop(regs);
  }
  EXPORT_SYMBOL(nmi_panic);
  
  /**
   *	panic - halt the system
   *	@fmt: The text string to print
   *
   *	Display a message, then perform cleanups.
   *
   *	This function never returns.
   */
  void panic(const char *fmt, ...)
  {
  	static char buf[1024];
  	va_list args;
  	long i, i_next = 0;
  	int state = 0;
  	int old_cpu, this_cpu;
  
  	/*
  	 * Disable local interrupts. This will prevent panic_smp_self_stop
  	 * from deadlocking the first cpu that invokes the panic, since
  	 * there is nothing to prevent an interrupt handler (that runs
  	 * after setting panic_cpu) from invoking panic() again.
  	 */
  	local_irq_disable();
  
  	/*
  	 * It's possible to come here directly from a panic-assertion and
  	 * not have preempt disabled. Some functions called from here want
  	 * preempt to be disabled. No point enabling it later though...
  	 *
  	 * Only one CPU is allowed to execute the panic code from here. For
  	 * multiple parallel invocations of panic, all other CPUs either
  	 * stop themself or will wait until they are stopped by the 1st CPU
  	 * with smp_send_stop().
  	 *
  	 * `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which
  	 * comes here, so go ahead.
  	 * `old_cpu == this_cpu' means we came from nmi_panic() which sets
  	 * panic_cpu to this CPU.  In this case, this is also the 1st CPU.
  	 */
  	this_cpu = raw_smp_processor_id();
  	old_cpu  = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
  
  	if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu)
  		panic_smp_self_stop();
  
  	console_verbose();
  	bust_spinlocks(1);
  	va_start(args, fmt);
  	vsnprintf(buf, sizeof(buf), fmt, args);
  	va_end(args);
  	pr_emerg("Kernel panic - not syncing: %s\n", buf);
  #ifdef CONFIG_DEBUG_BUGVERBOSE
  	/*
  	 * Avoid nested stack-dumping if a panic occurs during oops processing
  	 */
  	if (!test_taint(TAINT_DIE) && oops_in_progress <= 1)
  		dump_stack();
  #endif
  
  	/*
  	 * If we have crashed and we have a crash kernel loaded let it handle
  	 * everything else.
  	 * If we want to run this after calling panic_notifiers, pass
  	 * the "crash_kexec_post_notifiers" option to the kernel.
  	 */
  	if (!crash_kexec_post_notifiers)
  		crash_kexec(NULL);
  
  	/*
  	 * Note smp_send_stop is the usual smp shutdown function, which
  	 * unfortunately means it may not be hardened to work in a panic
  	 * situation.
  	 */
  	smp_send_stop();
  
  	/*
  	 * Run any panic handlers, including those that might need to
  	 * add information to the kmsg dump output.
  	 */
  	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
  
  	kmsg_dump(KMSG_DUMP_PANIC);
  
  	/*
  	 * If you doubt kdump always works fine in any situation,
  	 * "crash_kexec_post_notifiers" offers you a chance to run
  	 * panic_notifiers and dumping kmsg before kdump.
  	 * Note: since some panic_notifiers can make crashed kernel
  	 * more unstable, it can increase risks of the kdump failure too.
  	 */
  	if (crash_kexec_post_notifiers)
  		crash_kexec(NULL);
  
  	bust_spinlocks(0);
  
  	/*
  	 * We may have ended up stopping the CPU holding the lock (in
  	 * smp_send_stop()) while still having some valuable data in the console
  	 * buffer.  Try to acquire the lock then release it regardless of the
  	 * result.  The release will also print the buffers out.  Locks debug
  	 * should be disabled to avoid reporting bad unlock balance when
  	 * panic() is not being callled from OOPS.
  	 */
  	debug_locks_off();
  	console_flush_on_panic();
  
  	if (!panic_blink)
  		panic_blink = no_blink;
  
  	if (panic_timeout > 0) {
  		/*
  		 * Delay timeout seconds before rebooting the machine.
  		 * We can't use the "normal" timers since we just panicked.
  		 */
  		pr_emerg("Rebooting in %d seconds..", panic_timeout);
  
  		for (i = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) {
  			touch_nmi_watchdog();
  			if (i >= i_next) {
  				i += panic_blink(state ^= 1);
  				i_next = i + 3600 / PANIC_BLINK_SPD;
  			}
  			mdelay(PANIC_TIMER_STEP);
  		}
  	}
  	if (panic_timeout != 0) {
  		/*
  		 * This will not be a clean reboot, with everything
  		 * shutting down.  But if there is a chance of
  		 * rebooting the system it will be rebooted.
  		 */
  		emergency_restart();
  	}
  #ifdef __sparc__
  	{
  		extern int stop_a_enabled;
  		/* Make sure the user can actually press Stop-A (L1-A) */
  		stop_a_enabled = 1;
  		pr_emerg("Press Stop-A (L1-A) to return to the boot prom\n");
  	}
  #endif
  #if defined(CONFIG_S390)
  	{
  		unsigned long caller;
  
  		caller = (unsigned long)__builtin_return_address(0);
  		disabled_wait(caller);
  	}
  #endif
  	pr_emerg("---[ end Kernel panic - not syncing: %s\n", buf);
  	local_irq_enable();
  	for (i = 0; ; i += PANIC_TIMER_STEP) {
  		touch_softlockup_watchdog();
  		if (i >= i_next) {
  			i += panic_blink(state ^= 1);
  			i_next = i + 3600 / PANIC_BLINK_SPD;
  		}
  		mdelay(PANIC_TIMER_STEP);
  	}
  }
  
  EXPORT_SYMBOL(panic);
  
  
  struct tnt {
  	u8	bit;
  	char	true;
  	char	false;
  };
  
  static const struct tnt tnts[] = {
  	{ TAINT_PROPRIETARY_MODULE,	'P', 'G' },
  	{ TAINT_FORCED_MODULE,		'F', ' ' },
  	{ TAINT_CPU_OUT_OF_SPEC,	'S', ' ' },
  	{ TAINT_FORCED_RMMOD,		'R', ' ' },
  	{ TAINT_MACHINE_CHECK,		'M', ' ' },
  	{ TAINT_BAD_PAGE,		'B', ' ' },
  	{ TAINT_USER,			'U', ' ' },
  	{ TAINT_DIE,			'D', ' ' },
  	{ TAINT_OVERRIDDEN_ACPI_TABLE,	'A', ' ' },
  	{ TAINT_WARN,			'W', ' ' },
  	{ TAINT_CRAP,			'C', ' ' },
  	{ TAINT_FIRMWARE_WORKAROUND,	'I', ' ' },
  	{ TAINT_OOT_MODULE,		'O', ' ' },
  	{ TAINT_UNSIGNED_MODULE,	'E', ' ' },
  	{ TAINT_SOFTLOCKUP,		'L', ' ' },
  	{ TAINT_LIVEPATCH,		'K', ' ' },
  };
  
  /**
   *	print_tainted - return a string to represent the kernel taint state.
   *
   *  'P' - Proprietary module has been loaded.
   *  'F' - Module has been forcibly loaded.
   *  'S' - SMP with CPUs not designed for SMP.
   *  'R' - User forced a module unload.
   *  'M' - System experienced a machine check exception.
   *  'B' - System has hit bad_page.
   *  'U' - Userspace-defined naughtiness.
   *  'D' - Kernel has oopsed before
   *  'A' - ACPI table overridden.
   *  'W' - Taint on warning.
   *  'C' - modules from drivers/staging are loaded.
   *  'I' - Working around severe firmware bug.
   *  'O' - Out-of-tree module has been loaded.
   *  'E' - Unsigned module has been loaded.
   *  'L' - A soft lockup has previously occurred.
   *  'K' - Kernel has been live patched.
   *
   *	The string is overwritten by the next call to print_tainted().
   */
  const char *print_tainted(void)
  {
  	static char buf[ARRAY_SIZE(tnts) + sizeof("Tainted: ")];
  
  	if (tainted_mask) {
  		char *s;
  		int i;
  
  		s = buf + sprintf(buf, "Tainted: ");
  		for (i = 0; i < ARRAY_SIZE(tnts); i++) {
  			const struct tnt *t = &tnts[i];
  			*s++ = test_bit(t->bit, &tainted_mask) ?
  					t->true : t->false;
  		}
  		*s = 0;
  	} else
  		snprintf(buf, sizeof(buf), "Not tainted");
  
  	return buf;
  }
  
  int test_taint(unsigned flag)
  {
  	return test_bit(flag, &tainted_mask);
  }
  EXPORT_SYMBOL(test_taint);
  
  unsigned long get_taint(void)
  {
  	return tainted_mask;
  }
  
  /**
   * add_taint: add a taint flag if not already set.
   * @flag: one of the TAINT_* constants.
   * @lockdep_ok: whether lock debugging is still OK.
   *
   * If something bad has gone wrong, you'll want @lockdebug_ok = false, but for
   * some notewortht-but-not-corrupting cases, it can be set to true.
   */
  void add_taint(unsigned flag, enum lockdep_ok lockdep_ok)
  {
  	if (lockdep_ok == LOCKDEP_NOW_UNRELIABLE && __debug_locks_off())
  		pr_warn("Disabling lock debugging due to kernel taint\n");
  
  	set_bit(flag, &tainted_mask);
  }
  EXPORT_SYMBOL(add_taint);
  
  static void spin_msec(int msecs)
  {
  	int i;
  
  	for (i = 0; i < msecs; i++) {
  		touch_nmi_watchdog();
  		mdelay(1);
  	}
  }
  
  /*
   * It just happens that oops_enter() and oops_exit() are identically
   * implemented...
   */
  static void do_oops_enter_exit(void)
  {
  	unsigned long flags;
  	static int spin_counter;
  
  	if (!pause_on_oops)
  		return;
  
  	spin_lock_irqsave(&pause_on_oops_lock, flags);
  	if (pause_on_oops_flag == 0) {
  		/* This CPU may now print the oops message */
  		pause_on_oops_flag = 1;
  	} else {
  		/* We need to stall this CPU */
  		if (!spin_counter) {
  			/* This CPU gets to do the counting */
  			spin_counter = pause_on_oops;
  			do {
  				spin_unlock(&pause_on_oops_lock);
  				spin_msec(MSEC_PER_SEC);
  				spin_lock(&pause_on_oops_lock);
  			} while (--spin_counter);
  			pause_on_oops_flag = 0;
  		} else {
  			/* This CPU waits for a different one */
  			while (spin_counter) {
  				spin_unlock(&pause_on_oops_lock);
  				spin_msec(1);
  				spin_lock(&pause_on_oops_lock);
  			}
  		}
  	}
  	spin_unlock_irqrestore(&pause_on_oops_lock, flags);
  }
  
  /*
   * Return true if the calling CPU is allowed to print oops-related info.
   * This is a bit racy..
   */
  int oops_may_print(void)
  {
  	return pause_on_oops_flag == 0;
  }
  
  /*
   * Called when the architecture enters its oops handler, before it prints
   * anything.  If this is the first CPU to oops, and it's oopsing the first
   * time then let it proceed.
   *
   * This is all enabled by the pause_on_oops kernel boot option.  We do all
   * this to ensure that oopses don't scroll off the screen.  It has the
   * side-effect of preventing later-oopsing CPUs from mucking up the display,
   * too.
   *
   * It turns out that the CPU which is allowed to print ends up pausing for
   * the right duration, whereas all the other CPUs pause for twice as long:
   * once in oops_enter(), once in oops_exit().
   */
  void oops_enter(void)
  {
  	tracing_off();
  	/* can't trust the integrity of the kernel anymore: */
  	debug_locks_off();
  	do_oops_enter_exit();
  }
  
  /*
   * 64-bit random ID for oopses:
   */
  static u64 oops_id;
  
  static int init_oops_id(void)
  {
  #ifndef CONFIG_PREEMPT_RT_FULL
  	if (!oops_id)
  		get_random_bytes(&oops_id, sizeof(oops_id));
  	else
  #endif
  		oops_id++;
  
  	return 0;
  }
  late_initcall(init_oops_id);
  
  void print_oops_end_marker(void)
  {
  	init_oops_id();
  	pr_warn("---[ end trace %016llx ]---\n", (unsigned long long)oops_id);
  }
  
  /*
   * Called when the architecture exits its oops handler, after printing
   * everything.
   */
  void oops_exit(void)
  {
  	do_oops_enter_exit();
  	print_oops_end_marker();
  	kmsg_dump(KMSG_DUMP_OOPS);
  }
  
  #ifdef WANT_WARN_ON_SLOWPATH
  struct slowpath_args {
  	const char *fmt;
  	va_list args;
  };
  
  static void warn_slowpath_common(const char *file, int line, void *caller,
  				 unsigned taint, struct slowpath_args *args)
  {
  	disable_trace_on_warning();
  
  	pr_warn("------------[ cut here ]------------\n");
  	pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS()\n",
  		raw_smp_processor_id(), current->pid, file, line, caller);
  
  	if (args)
  		vprintk(args->fmt, args->args);
  
  	if (panic_on_warn) {
  		/*
  		 * This thread may hit another WARN() in the panic path.
  		 * Resetting this prevents additional WARN() from panicking the
  		 * system on this thread.  Other threads are blocked by the
  		 * panic_mutex in panic().
  		 */
  		panic_on_warn = 0;
  		panic("panic_on_warn set ...\n");
  	}
  
  	print_modules();
  	dump_stack();
  	print_oops_end_marker();
  	/* Just a warning, don't kill lockdep. */
  	add_taint(taint, LOCKDEP_STILL_OK);
  }
  
  void warn_slowpath_fmt(const char *file, int line, const char *fmt, ...)
  {
  	struct slowpath_args args;
  
  	args.fmt = fmt;
  	va_start(args.args, fmt);
  	warn_slowpath_common(file, line, __builtin_return_address(0),
  			     TAINT_WARN, &args);
  	va_end(args.args);
  }
  EXPORT_SYMBOL(warn_slowpath_fmt);
  
  void warn_slowpath_fmt_taint(const char *file, int line,
  			     unsigned taint, const char *fmt, ...)
  {
  	struct slowpath_args args;
  
  	args.fmt = fmt;
  	va_start(args.args, fmt);
  	warn_slowpath_common(file, line, __builtin_return_address(0),
  			     taint, &args);
  	va_end(args.args);
  }
  EXPORT_SYMBOL(warn_slowpath_fmt_taint);
  
  void warn_slowpath_null(const char *file, int line)
  {
  	warn_slowpath_common(file, line, __builtin_return_address(0),
  			     TAINT_WARN, NULL);
  }
  EXPORT_SYMBOL(warn_slowpath_null);
  #endif
  
  #ifdef CONFIG_CC_STACKPROTECTOR
  
  /*
   * Called when gcc's -fstack-protector feature is used, and
   * gcc detects corruption of the on-stack canary value
   */
  __visible void __stack_chk_fail(void)
  {
  	panic("stack-protector: Kernel stack is corrupted in: %p\n",
  		__builtin_return_address(0));
  }
  EXPORT_SYMBOL(__stack_chk_fail);
  
  #endif
  
  core_param(panic, panic_timeout, int, 0644);
  core_param(pause_on_oops, pause_on_oops, int, 0644);
  core_param(panic_on_warn, panic_on_warn, int, 0644);
  
  static int __init setup_crash_kexec_post_notifiers(char *s)
  {
  	crash_kexec_post_notifiers = true;
  	return 0;
  }
  early_param("crash_kexec_post_notifiers", setup_crash_kexec_post_notifiers);
  
  static int __init oops_setup(char *s)
  {
  	if (!s)
  		return -EINVAL;
  	if (!strcmp(s, "panic"))
  		panic_on_oops = 1;
  	return 0;
  }
  early_param("oops", oops_setup);
  