vprintk

#ifdef CONFIG_PRINTK_NMI
/*
 * Safe printk() for NMI context. It uses a per-CPU buffer to
 * store the message. NMIs are not nested, so there is always only
 * one writer running. But the buffer might get flushed from another
 * CPU, so we need to be careful.
 */
static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
{
    struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
 
    return printk_safe_log_store(s, fmt, args);
}
 
void notrace printk_nmi_enter(void)
{
    this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
}
 
void notrace printk_nmi_exit(void)
{
    this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
}
 
/*
 * Marks a code that might produce many messages in NMI context
 * and the risk of losing them is more critical than eventual
 * reordering.
 *
 * It has effect only when called in NMI context. Then printk()
 * will try to store the messages into the main logbuf directly
 * and use the per-CPU buffers only as a fallback when the lock
 * is not available.
 */
void printk_nmi_direct_enter(void)
{
    if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
        this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
}
 
void printk_nmi_direct_exit(void)
{
    this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
}
 
#else
 
static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
{
    return 0;
}
函数源码
