Linux Panic 机制解析

1.panic 操作

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2.panic函数

主要功能：内核出现异常的时候输出异常信息，异常栈信息，挂起系统，代码主要流程和上面的流程图一致

/**
 *	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;

	/*
	 * 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();  /*同一时间只有一个核能执行panic代码，获取到锁的cpu先把自己stop掉，其他核要么自己stop自己  要么等待拿到锁的核执行smp_send_stop*/

	console_verbose();/* 提高打印等级 */

	bust_spinlocks(1); /*bust_spinlocks()机制,用来避免系统crash以至于无法正常工作的时候还要进行不必要的等待spinlock操作*/

	va_start(args, fmt);
    /* 利用va_start指针遍历函数栈方式处理多参数
     * 函数栈: (高地址)|-最后一个参数--... ...--第一个参数-|---返回地址---|---函数执行代码-      --|（低地址）
     */
	vsnprintf(buf, sizeof(buf), fmt, args);
	va_end(args);

	printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
#ifdef CONFIG_DEBUG_BUGVERBOSE        /* 是否输出BUG行号和文件名 */
	/*
	 * Avoid nested stack-dumping if a panic occurs during oops processing
	 */
	if (!test_taint(TAINT_DIE) && oops_in_progress <= 1)
		dump_stack();   /*打印堆栈*/
#endif

	/*
	 * If we have crashed and we have a crash kernel loaded let it handle
	 * everything else.
	 * Do we want to call this before we try to display a message?
	 */
	crash_kexec(NULL);/* 内核crash的操作 */

	kmsg_dump(KMSG_DUMP_PANIC);/*kmsg日志保存到mtd设备去，需要提前分配好mtd存储*/

	/*
	 * 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(); /* 停止其他多核的工作 */

	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);/*注册了异常handle的函数都调用一次*/

	bust_spinlocks(0);

	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.
		 */
		printk(KERN_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();
	}

    /**
     *  panic_timeout = 0 进行死循环，抢占被禁止，CPU一直运行panic程序中运行。
     */
	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);

3. panic的打印和排查

①        内核代码可以放开 CONFIG_DEBUG_BUGVERBOSE宏，输出问题代码文件和位置，还可以了使用gdb打断点来排查

②        内核模块使用反汇编objdump -S XXX.o -g 可以将反汇编和代码放在一起比较

参考文章：

Kernel函数解析之panic_小小小小小小小小熊的博客-CSDN博客_kernel panic位置：panic()函数在panic.c文件中，该文件位于kernel/目录下；作用：该函数的主要作用是停止当前的系统运行，供系统监测到异常时调用。流程：【源码】：/** *panic - halt the system *@fmt: The text string to print * *Display a message, then perform cleanups. * *This function never returns. */void panic.https://blog.csdn.net/lixiaojie1012/article/details/119703588panic函数分析-xlzxlz2-ChinaUnix博客在阅读协议栈代码（内核版本2.6.38），在很多地方都看到panic调用，只是知道大体功能，从未具体分析过，也一直想把协议栈的分析过程写下来，很懒，就一有写，算今天是个开始吧。分析panic太艰难啦，涉及的东西太多啦。/** http://blog.chinaunix.net/uid-26377382-id-4913475.htmlkernel panic 分析解决方法_jerry_chg的博客-CSDN博客_kernel panickernel panic 表示Linux kernel走到了一个不知道该怎么走下一步的状况，一旦到这个情况，kernel就尽可能把它此时能获取的全部信息都打印出来，至于能打印出多少信息。 下面讲解几种用于查找出错函数定位的方法首先看一下出错的kernel panic 现象，下面是一个kernel panic的出错log：https://jerry-cheng.blog.csdn.net/article/details/19172725?spm=1001.2101.3001.6650.2&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-2-19172725-blog-119703588.pc_relevant_default&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-2-19172725-blog-119703588.pc_relevant_default&utm_relevant_index=5kernel crash 发生后的那些事（四）_shuai_wen的博客-CSDN博客