lkml.org 
[lkml]   [2020]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v7 3/3] leds: trigger: implement a tty trigger
On Tue, Jul 21, 2020 at 09:48:15PM +0200, Uwe Kleine-König wrote:
> Hello Johan,
>
> On Tue, Jul 14, 2020 at 09:13:55AM +0200, Johan Hovold wrote:
> > On Tue, Jul 07, 2020 at 06:59:58PM +0200, Uwe Kleine-König wrote:
> > > + while (firstrun ||
> > > + icount.rx != trigger_data->rx ||
> > > + icount.tx != trigger_data->tx) {
> > > +
> > > + led_set_brightness(trigger_data->led_cdev, LED_ON);
> > > +
> > > + msleep(100);
> > > +
> > > + led_set_brightness(trigger_data->led_cdev, LED_OFF);
> > > +
> > > + trigger_data->rx = icount.rx;
> > > + trigger_data->tx = icount.tx;
> > > + firstrun = false;
> > > +
> > > + ret = tty_get_icount(trigger_data->tty, &icount);
> > > + if (ret)
> > > + return;
> > > + }
> >
> > Haven't looked at the latest proposal in detail, but this looks broken
> > as you can potentially loop indefinitely in a worker thread, and with no
> > way to stop the trigger (delayed work).
>
> I don't think that potentially looping indefinitely is a problem, but
> indeed it should drop the lock during each iteration. Will think about
> how to adapt.

You musn't queue work that can run for long on the global shared
workqueue as it affects flushing:

* system_wq is the one used by schedule[_delayed]_work[_on]().
* Multi-CPU multi-threaded. There are users which expect relatively
* short queue flush time. Don't queue works which can run for too
* long.

Work that potentially run indefinitely is an absolute no-no. :)

Johan
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2020-07-22 10:34    [W:0.052 / U:0.412 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site