第21章 Linux设备驱动的调试之BUG_ON（）和WARN_ON（）

21.7　BUG_ON（）和WARN_ON（）

    内核中有许多地方调用类似BUG（）的语句，它非常像一个内核运行时的断言，意味着本来不该执行到BUG（）这条语句，一旦执行即抛出Oops。BUG（）的定义为：

include/asm-generic/bug.h

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

其中panic（）定义在kernel/panic.c中，会导致内核崩溃，并打印Oops。

/**
 * 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;
bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;

/*
* 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.