Messages in this thread | | | Date | Fri, 1 Apr 2016 17:00:32 +0200 | From | Petr Mladek <> | Subject | Re: [RFC][PATCH v9 1/2] printk: Make printk() completely async |
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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 <pmladek@suse.com>
Best Regards, Petr
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