On (03/21/16 16:33), Jan Kara wrote:
[..]
> > > And by calling wake_up_process() under logbuf_lock, you actually introduce
> > > recursion issues for printk_deferred() messages which are supposed to be
> > > working from under rq->lock and similar. So I think you have to keep this
> > > section outside of logbuf_lock.
> >
> > hm, in_sched (printk_deferred()) messages are printed by
> > irq work->wake_up_klogd_work_func(), not by wake_up_process()
> > from vprintk_emit(). or am I missing something?
>
> Think of following:
>
> some function
> printk()
> vprintk_emit()
> spin_lock(&logbuf_lock);
> ...
> wake_up_process()
> printk_deferred()
> vprintk_emit() -> recursion on logbuf_lock
uh, indeed. I was more concerned about printk() calls that are
troublemakers and are already in wake_up_process() - spin_dump()s.
but yes, braking printk_deferred() in this case is a regression.
thanks for pointing that out. and also thanks to Byungchul.
-ss
> Previously scheduler code was allowed to call printk_deferred() wherever it
> wanted...
>
> So we are not supposed to call into the scheduler from under logbuf_lock...
>
> Honza
> --
> Jan Kara <j...@suse.com>
> SUSE Labs, CR
>
