On Wed 2016-03-23 09:37:25, Sergey Senozhatsky wrote:
> Hello Petr,
>
> On (03/22/16 14:11), Petr Mladek wrote:
> > > + * Set printing_func() sleep condition early, under the @logbuf_lock.
> > > + * So printing kthread (if RUNNING) will go to console_lock() and spin
> > > + * on @logbuf_lock.
> > > + */
> > > + if (!printk_sync)
> > > + need_flush_console = true;
> >
> > We set this variable for each call and also when printk_kthread is
> > NULL or when sync_printk is false.
>
> hm, yes. (printk_kthread && !need_flush_console) makes more sense.
> so we it doesn't get re-dirty if already set.
This does not solve the problem mentioned below. There still might be
extra cycle if the kthread is inside console_unclock().
> > We migth want to clear it also from console_unlock(). I think that
> > a good place would be in the check:
> >
> > raw_spin_lock(&logbuf_lock);
> > retry = console_seq != log_next_seq;
> > raw_spin_unlock_irqrestore(&logbuf_lock, flags);
>
> hm, what's wrong with clearing it in printk_kthread printing function?
I though about the following scenario:
CPU0 CPU1
vprintk_emit()
need_flush_console = true;
wake_up_process(printk_thread)
printing_func()
need_flush_console = false;
console_lock()
console_unlock()
vprintk_emit()
need_flush_console = true;
# flush 1st message
# flush 2nd message
if (!need_flush_console)
# fails and continues
console_lock()
console_unlock()
# nope because 2nd
# message already flushed
if (!need_flush_console)
schedule()
# did one unnecessary
# cycle to get asleep
Best Regards,
Petr
PS: If you touch the code, please rename printing_func() to
printk_kthread_func() to make it more clear what it does.
I am sorry for nitpicking.
