Re: [PATCH 2/2] Subject: printk: Don't trap random context in infinite log_buf flush

Tejun Heo
2017-11-08T14:33:41Z

Hello,

On Wed, Nov 08, 2017 at 02:29:35PM +0900, Sergey Senozhatsky wrote:
> > The following is a completely untested patch to show how we can put
> > the console in full sync mode, just the general idea. I'm a bit
> > skeptical we really wanna do this given that we already (with or
> > without the patch) stay sync for most of these events due to the way
> > we go async, but, yeah, if we wanna do that, we can do that.
>
> we've been going in a slightly different direction in printk-kthread.
>
> we keep printk sync by default [as opposed to previous "immediately
> offload" approach]. people asked for it, some people demanded it. we
> offload to printk-kthread only when we detect that this particular
> task on this particular CPU has been doing printing (without rescheduling)
> for 1/2 of watchdog threshold value. IOW, if we see that we are heading
> towards the lockup limit then we offload. otherwise - we let it loop in
> console_unlock().

FWIW, I'm still a bit skeptical whether that's the right direction.
People asking for it doesn't indicate that the flipside isn't worse.
Hmm... I think my impression is mostly from the fact that throughout
the years I can only count few times where loss of printk messages was
an actual issue. The system getting slowed down / locking up from
printk message deluge was *far* more prevalent.

Thanks.

--
tejun