Re: [RFC][PATCH v6 1/2] printk: Make printk() completely async

From: Petr Mladek
Date: Tue Mar 22 2016 - 12:36:34 EST


On Tue 2016-03-22 02:25:29, Sergey Senozhatsky wrote:
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index e38579d..99c105d6 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1619,12 +1721,21 @@ asmlinkage int vprintk_emit(int facility, int level,
> int printed_len = 0;
> int nmi_message_lost;
> bool in_sched = false;
> - /* cpu currently holding logbuf_lock in this function */
> - static unsigned int logbuf_cpu = UINT_MAX;
> + bool in_panic = console_loglevel == CONSOLE_LOGLEVEL_MOTORMOUTH;

I am just looking at the printk in NMI patchset and I will need to
deal with the panic state as well. I am not sure if this detection
is secure.

This console level is set also by kdb_show_stack()
and kdb_dumpregs(). I am not sure how this kdb stuff works
and if it affects normal kernel but...

Anyway, it seems that many locations detects the panic situation
via the variable oops_in_progress. It has another advantage
that it can be easily checked and we would not need any extra
variable here.


> + bool sync_print = printk_sync;
> +
> + /* disable async printk */
> + if (in_panic)
> + printk_sync = true;

In each case, we should not switch the global state if we
only print debug traces.

Best Regards,
Petr