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.
Thanks,
Guenter
> ---
> drivers/watchdog/softdog.c | 40 ++++++++++++++++++++++++----------------
> 1 file changed, 24 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/watchdog/softdog.c b/drivers/watchdog/softdog.c
> index c7bdc986dca1..0f67cd068465 100644
> --- a/drivers/watchdog/softdog.c
> +++ b/drivers/watchdog/softdog.c
> @@ -21,13 +21,12 @@
>
> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>
> +#include <linux/hrtimer.h>
> #include <linux/init.h>
> -#include <linux/jiffies.h>
> #include <linux/kernel.h>
> #include <linux/module.h>
> #include <linux/moduleparam.h>
> #include <linux/reboot.h>
> -#include <linux/timer.h>
> #include <linux/types.h>
> #include <linux/watchdog.h>
>
> @@ -54,7 +53,10 @@ module_param(soft_panic, int, 0);
> MODULE_PARM_DESC(soft_panic,
> "Softdog action, set to 1 to panic, 0 to reboot (default=0)");
>
> -static void softdog_fire(unsigned long data)
> +static struct hrtimer softdog_ticktock;
> +static struct hrtimer softdog_preticktock;
> +
> +static enum hrtimer_restart softdog_fire(struct hrtimer *timer)
> {
> module_put(THIS_MODULE);
> if (soft_noboot) {
> @@ -67,41 +69,42 @@ static void softdog_fire(unsigned long data)
> emergency_restart();
> pr_crit("Reboot didn't ?????\n");
> }
> -}
>
> -static struct timer_list softdog_ticktock =
> - TIMER_INITIALIZER(softdog_fire, 0, 0);
> + return HRTIMER_NORESTART;
> +}
>
> static struct watchdog_device softdog_dev;
>
> -static void softdog_pretimeout(unsigned long data)
> +static enum hrtimer_restart softdog_pretimeout(struct hrtimer *timer)
> {
> watchdog_notify_pretimeout(&softdog_dev);
> -}
>
> -static struct timer_list softdog_preticktock =
> - TIMER_INITIALIZER(softdog_pretimeout, 0, 0);
> + return HRTIMER_NORESTART;
> +}
>
> static int softdog_ping(struct watchdog_device *w)
> {
> - if (!mod_timer(&softdog_ticktock, jiffies + (w->timeout * HZ)))
> + if (!hrtimer_active(&softdog_ticktock))
> __module_get(THIS_MODULE);
> + hrtimer_start(&softdog_ticktock, ktime_set(w->timeout, 0),
> + HRTIMER_MODE_REL);
>
> if (w->pretimeout)
> - mod_timer(&softdog_preticktock, jiffies +
> - (w->timeout - w->pretimeout) * HZ);
> + hrtimer_start(&softdog_preticktock,
> + ktime_set(w->timeout - w->pretimeout, 0),
> + HRTIMER_MODE_REL);
> else
> - del_timer(&softdog_preticktock);
> + hrtimer_cancel(&softdog_preticktock);
>
> return 0;
> }
>
> static int softdog_stop(struct watchdog_device *w)
> {
> - if (del_timer(&softdog_ticktock))
> + if (hrtimer_cancel(&softdog_ticktock))
> module_put(THIS_MODULE);
>
> - del_timer(&softdog_preticktock);
> + hrtimer_cancel(&softdog_preticktock);
>
> return 0;
> }
> @@ -134,6 +137,11 @@ static int __init softdog_init(void)
> watchdog_set_nowayout(&softdog_dev, nowayout);
> watchdog_stop_on_reboot(&softdog_dev);
>
> + hrtimer_init(&softdog_ticktock, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + softdog_ticktock.function = softdog_fire;
> + hrtimer_init(&softdog_preticktock, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + softdog_preticktock.function = softdog_pretimeout;
> +
> ret = watchdog_register_device(&softdog_dev);
> if (ret)
> return ret;
--
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