Linux下的dump_stack

当kernel出现错误时，会打印堆栈信息，我们可以根据信息追溯问题的来源，该函数实行如下

/**
 * dump_stack - dump the current task information and its stack trace
 *
 * Architectures can override this implementation by implementing its own.
 */
#ifdef CONFIG_SMP
static atomic_t dump_lock = ATOMIC_INIT(-1);

asmlinkage __visible void dump_stack(void)
{
	unsigned long flags;
	int was_locked;
	int old;
	int cpu;

	/*
	 * Permit this cpu to perform nested stack dumps while serialising
	 * against other CPUs
	 */
retry:
	local_irq_save(flags);
	cpu = smp_processor_id();
	old = atomic_cmpxchg(&dump_lock, -1, cpu);
	if (old == -1) {
		was_locked = 0;
	} else if (old == cpu) {
		was_locked = 1;
	} else {
		local_irq_restore(flags);
		cpu_relax();
		goto retry;
	}

	__dump_stack();

	if (!was_locked)
		atomic_set(&dump_lock, -1);

	local_irq_restore(flags);
}
#else
asmlinkage __visible void dump_stack(void)
{
	__dump_stack();
}
#endif
EXPORT_SYMBOL(dump_stack);

在追踪代码的调用时，我们也可以使用dump_stack函数来辅助我们分析。

类似的函数还有BUG,BUG_ON,WARN,WANR_ON。

调用BUG/BUG_ON会导致系统死机，注意

在没定义HAVE_ARCH_BUG_ON，BUG定义如下

#ifdef CONFIG_BUG
#ifndef HAVE_ARCH_BUG
#define BUG() do { \
	printk("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
	panic("BUG!"); \
} while (0)
#endif

#ifndef HAVE_ARCH_BUG_ON
#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
#endif
#endif

/**
 *	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 DEFINE_SPINLOCK(panic_lock);
	static char buf[1024];
	va_list args;
	long i, i_next = 0;
	int state = 0;

	/*
	 * 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 the panic_lock is acquired) 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().
	 */
	if (!spin_trylock(&panic_lock))
		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

#ifdef CONFIG_SPRD_SYSDUMP
	sysdump_enter(0,buf,NULL);
#else
	/*
	 * 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();
#endif
	/*
	 * 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..\n", 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);

默认都有定义 arch/arm/include/asm/bug.h 

#define BUG() _BUG(__FILE__, __LINE__, BUG_INSTR_VALUE)
#define _BUG(file, line, value) __BUG(file, line, value)
#ifdef CONFIG_DEBUG_BUGVERBOSE

/*
 * The extra indirection is to ensure that the __FILE__ string comes through
 * OK. Many version of gcc do not support the asm %c parameter which would be
 * preferable to this unpleasantness. We use mergeable string sections to
 * avoid multiple copies of the string appearing in the kernel image.
 */

#define __BUG(__file, __line, __value)				\
do {								\
	asm volatile("1:\t" BUG_INSTR(__value) "\n"  \
		".pushsection .rodata.str, \"aMS\", %progbits, 1\n" \
		"2:\t.asciz " #__file "\n" 			\
		".popsection\n" 				\
		".pushsection __bug_table,\"a\"\n"		\
		".align 2\n"					\
		"3:\t.word 1b, 2b\n"				\
		"\t.hword " #__line ", 0\n"			\
		".popsection");					\
	unreachable();						\
} while (0)

 

#define WARN(condition, format...) ({						\
	int __ret_warn_on = !!(condition);				\
	if (unlikely(__ret_warn_on))					\
		__WARN_printf(format);					\
	unlikely(__ret_warn_on);					\
})

#ifndef WARN_ON
#define WARN_ON(condition) ({						\
	int __ret_warn_on = !!(condition);				\
	if (unlikely(__ret_warn_on))					\
		__WARN();						\
	unlikely(__ret_warn_on);					\
})
#endif

#define __WARN()		warn_slowpath_null(__FILE__, __LINE__)

void warn_slowpath_null(const char *file, int line)
{
	warn_slowpath_common(file, line, __builtin_return_address(0),
			     TAINT_WARN, NULL);
}

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);
}