Re: watchdog: softdog: fire watchdog even if softirqs do not get to run

[Guenter Roeck]

On 02/27/2017 04:58 AM, Niklas Cassel wrote:
> On 02/27/2017 05:04 AM, Guenter Roeck wrote:
> > On Fri, Feb 17, 2017 at 07:25:02PM +0100, Niklas Cassel wrote:
> > > From: Niklas Cassel <niklas.cassel@xxxxxxxx>
> > >
> > > Checking for timer expiration is done from the softirq TIMER_SOFTIRQ.
> > >
> > > Since commit 4cd13c21b207 ("softirq: Let ksoftirqd do its job"),
> > > pending softirqs are no longer always handled immediately, instead,
> > > if there are pending softirqs, and ksoftirqd is in state TASK_RUNNING,
> > > the handling of the softirqs are deferred, and are instead supposed
> > > to be handled by ksoftirqd, when ksoftirqd gets scheduled.
> > >
> > > If a user space process with a real-time policy starts to misbehave
> > > by never relinquishing the CPU while ksoftirqd is in state TASK_RUNNING,
> > > what will happen is that all softirqs will get deferred, while ksoftirqd,
> > > which is supposed to handle the deferred softirqs, will never get to run.
> > >
> > > To make sure that the watchdog is able to fire even when we do not get
> > > to run softirqs, replace the timers with hrtimers.
> > >
> > > Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxx>
> > > Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Niklas,
> >
> > Please rebase onto current mainline, test, and resubmit.
>
> I've sent out a v2 now :)
>
> Although, I thought that it was a bit weird that the conflicting patch
> was in Linus tree but is not in next-20170227.
It was in the watchdog-next branch of my repository at kernel.org,
which is not in -next. I'll have to sort that out with Wim at some point.

> I'm not sure if you are the web master for www.linux-watchdog.org,
> but their cgit seems to be broken:
> http://www.linux-watchdog.org/cgi-bin/gitweb.cgi?p=linux-watchdog.git;a=summary
> http://www.linux-watchdog.org/cgi-bin/gitweb.cgi?p=linux-watchdog-next.git;a=summary
Wim knows about it, and plans to replace the server.

Guenter