On Fri 2016-04-01 23:10:04, Sergey Senozhatsky wrote:
> This patch makes printk() completely asynchronous (similar to what
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index bfbf284..2e50c48 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2722,6 +2761,47 @@ static int __init printk_late_init(void)
> late_initcall(printk_late_init);
>
> #if defined CONFIG_PRINTK
> +static int printk_kthread_func(void *data)
> +{
> + while (1) {
> + set_current_state(TASK_INTERRUPTIBLE);
> + if (!printk_kthread_need_flush_console)
> + schedule();
> +
> + __set_current_state(TASK_RUNNING);
> +
> + console_lock();
> + console_unlock();
> + /*
> + * Avoid an infinite loop when console_unlock() cannot
> + * access consoles, e.g. because console_suspended is
> + * true. schedule(), someone else will print the messages
> + * from resume_console().
> + */
> + printk_kthread_need_flush_console = false;
You need to move this assigment right above the console_lock()/console_unlock()
calls. Otherwise, there is a race:
CPU0: CPU1
printk_kthread_func()
console_unlock()
printk()
printk_kthread_need_flush_console = true;
wake_up_process(printk_kthread);
printk_kthread_need_flush_console = false;
set_current_state(TASK_INTERRUPTIBLE);
if (!printk_kthread_need_flush_console)
schedule();
=> sleeping without processing the last message.
You could safely set it false before calling
console_lock()/console_unlock() because you are calling the commands
that are requested by the flag.
With the above described change:
Reviewed-by: Petr Mladek <pmla...@suse.com>
Best Regards,
Petr
