Linux : kernel code : printk.c

linux/kernel.h

#define KERN_EMERG      "<0>"   /* system is unusable                   */
#define KERN_ALERT      "<1>"   /* action must be taken immediately     */
#define KERN_CRIT       "<2>"   /* critical conditions                  */
#define KERN_ERR        "<3>"   /* error conditions                     */
#define KERN_WARNING    "<4>"   /* warning conditions                   */
#define KERN_NOTICE     "<5>"   /* normal but significant condition     */
#define KERN_INFO       "<6>"   /* informational                        */
#define KERN_DEBUG      "<7>"   /* debug-level messages                 */

kernel/panic.c

NORET_TYPE void panic(const char * fmt, ...)
{
        static char buf[1024];
        va_list args;
        long i;

        /*
         * 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...
         */
        preempt_disable();

        bust_spinlocks(1);
        va_start(args, fmt);
        vsnprintf(buf, sizeof(buf), fmt, args);
        va_end(args);
        printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);



kernel/printk.c

asmlinkage int printk(const char *fmt, ...)
{
        va_list args;
        int r;

        va_start(args, fmt);
        r = vprintk(fmt, args);
        va_end(args);

        return r;
}

asmlinkage int vprintk(const char *fmt, va_list args)
{
        int printed_len = 0;
        int current_log_level = default_message_loglevel;
        unsigned long flags;
        int this_cpu;
        char *p;

        boot_delay_msec();
        printk_delay();

        preempt_disable();
        /* This stops the holder of console_sem just where we want him */
        raw_local_irq_save(flags);
        this_cpu = smp_processor_id();

        /*
         * Ouch, printk recursed into itself!
         */
        if (unlikely(printk_cpu == this_cpu)) {
                /*
                 * If a crash is occurring during printk() on this CPU,