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

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Message-ID: <e550bcd0-2628-080a-c04c-f15623055a67@axis.com>
Date:   Mon, 27 Feb 2017 13:58:20 +0100
From:   Niklas Cassel <niklas.cassel@...s.com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     <wim@...ana.be>, <edumazet@...gle.com>, <peterz@...radead.org>,
        <linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: watchdog: softdog: fire watchdog even if softirqs do not get to
 run

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@...s.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@...s.com>
>> Reviewed-by: Guenter Roeck <linux@...ck-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.

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


>
> Thanks,
> Guenter
>