Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

[Petr Mladek]

On Thu 2018-01-11 19:38:45, Sergey Senozhatsky wrote:
> On (01/11/18 10:34), Petr Mladek wrote:
> [..]
> > > except that handing off a console_sem to atomic task when there
> > > is   O(logbuf) > watchdog_thresh   is a regression, basically...
> > > it is what it is.
> > 
> > How this could be a regression? Is not the victim that handles
> > other printk's random? What protected the atomic task to
> > handle the other printks before this patch?
> 
> the non-atomic -> atomic context console_sem transfer. we previously
> would have kept the console_sem owner to its non-atomic owner. we now
> will make sure that if printk from atomic context happens then it will
> make it to console_unlock() loop.
> emphasis on O(logbuf) > watchdog_thresh.

Sergey, please, why do you completely and repeatedly ignore that
argument about statistical effects?

Yes, the above scenario is possible. But Steven's patch might also move the
owner from atomic context to a non-atomic one. The chances should be
more or less equal. The main advantage is that the owner is moved.
This should statistically lower the chance of a soft-lockup.

> 
> > Or do you have a system that started to suffer from softlockups
> > with this patchset and did not do this before?
> [..]
> > Do you know about any system where this patch made the softlockup
> > deterministically or statistically more likely, please?
> 
> I have explained many, many times why my boards die just like before.
> why would I bother collecting any numbers...

Is it with your own printk stress tests or during "normal" work?

If it is during a normal work, is there any chance that we
could have a look at the logs?

Best Regards,
Petr