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

From	Guenter Roeck <linux@roeck-us.net>
Newsgroups	linux.kernel
Subject	Re: watchdog: softdog: fire watchdog even if softirqs do not get to run
Date	2017-02-27 15:40 +0100
Message-ID	<tfuD0-6Rb-5@gated-at.bofh.it> (permalink)
References	<tbVs5-7Mv-3@gated-at.bofh.it> <tfkNj-8pE-3@gated-at.bofh.it> <tftdT-5Yo-1@gated-at.bofh.it>
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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@axis.com>
>>>
>>> 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@axis.com>
>>> Reviewed-by: Guenter Roeck <linux@roeck-us.net>
>> 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

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[PATCH] watchdog: softdog: fire watchdog even if softirqs do not get to run Niklas Cassel <niklas.cassel@axis.com> - 2017-02-17 19:30 +0100
  Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not  get to run Guenter Roeck <linux@roeck-us.net> - 2017-02-19 18:40 +0100
    Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not  get to run Peter Zijlstra <peterz@infradead.org> - 2017-02-20 09:40 +0100
      Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not  get to run Guenter Roeck <linux@roeck-us.net> - 2017-02-20 11:50 +0100
    Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not  get to run Niklas Cassel <niklas.cassel@axis.com> - 2017-02-20 11:10 +0100
      Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not  get to run Guenter Roeck <linux@roeck-us.net> - 2017-02-20 16:40 +0100
  Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not  get to run Guenter Roeck <linux@roeck-us.net> - 2017-02-20 16:40 +0100
  Re: watchdog: softdog: fire watchdog even if softirqs do not get to  run Guenter Roeck <linux@roeck-us.net> - 2017-02-27 05:10 +0100
    Re: watchdog: softdog: fire watchdog even if softirqs do not get to  run Niklas Cassel <niklas.cassel@axis.com> - 2017-02-27 14:10 +0100
      Re: watchdog: softdog: fire watchdog even if softirqs do not get to  run Guenter Roeck <linux@roeck-us.net> - 2017-02-27 15:40 +0100

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