On (06/27/18 16:20), Petr Mladek wrote:
> +/*
> + * 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);
> +}
A side note: This nesting also handles recursive printk-s for us.
NMI:
printk_nmi_enter
ftrace_dump
printk_nmi_direct_enter
vprintk_func
spin_lock(logbuf_lock)
vprintk_store
vsprintf
WARN_ON
vprintk_func
vprintk_nmi
> __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
> {
> + /*
> + * Try to use the main logbuf even in NMI. But avoid calling console
> + * drivers that might have their own locks.
> + */
> + if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
> + raw_spin_trylock(&logbuf_lock)) {
> + int len;
> +
> + len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
> + raw_spin_unlock(&logbuf_lock);
> + defer_console();
> + return len;
> + }
So, maybe, something a bit better than defer_console().
Otherwise,
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
-ss
