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
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