Messages in this thread | | | Subject | Re: [PATCH] watchdog: softdog: fire watchdog even if softirqs do not get to run | From | Guenter Roeck <> | Date | Mon, 20 Feb 2017 01:02:24 -0800 |
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On 02/20/2017 12:36 AM, Peter Zijlstra wrote: > On Sun, Feb 19, 2017 at 08:46:28AM -0800, Guenter Roeck wrote: >> Cc: Wolfram for input. >> >> On 02/17/2017 10:25 AM, 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. >>> >> >> This makes the driver dependent on HIGH_RES_TIMERS, which is not available >> on all architectures. Before adding that restriction, I would like to see >> some discussion if this is the only feasible solution. >> > > It does no such thing; the hrtimer interface is always available. >
That is good to hear. Thanks for the correction.
Guenter
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