Linux Panic 机制解析

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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.（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。/** .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：=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