From a19f89335f4bda3d77d991c96583e3e51856acbb Mon Sep 17 00:00:00 2001 From: Julia Cartwright Date: Tue, 5 Nov 2019 15:45:06 +0100 Subject: watchdog: prevent deferral of watchdogd wakeup on RT When PREEMPT_RT is enabled, all hrtimer expiry functions are deferred for execution into the context of ksoftirqd unless otherwise annotated. Deferring the expiry of the hrtimer used by the watchdog core, however, is a waste, as the callback does nothing but queue a kthread work item and wakeup watchdogd. It's worst then that, too: the deferral through ksoftirqd also means that for correct behavior a user must adjust the scheduling parameters of both watchdogd _and_ ksoftirqd, which is unnecessary and has other side effects (like causing unrelated expiry functions to execute at potentially elevated priority). Instead, mark the hrtimer used by the watchdog core as being _HARD to allow it's execution directly from hardirq context. The work done in this expiry function is well-bounded and minimal. A user still must adjust the scheduling parameters of the watchdogd to be correct w.r.t. their application needs. Link: https://lkml.kernel.org/r/0e02d8327aeca344096c246713033887bc490dd7.1538089180.git.julia@ni.com Cc: Guenter Roeck Reported-and-tested-by: Steffen Trumtrar Reported-by: Tim Sander Signed-off-by: Julia Cartwright Acked-by: Guenter Roeck [bigeasy: use only HRTIMER_MODE_REL_HARD] Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Guenter Roeck Link: https://lore.kernel.org/r/20191105144506.clyadjbvnn7b7b2m@linutronix.de Signed-off-by: Guenter Roeck Signed-off-by: Wim Van Sebroeck --- drivers/watchdog/watchdog_dev.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c index 55db4c95f0e8..62483a99105c 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -157,7 +157,8 @@ static inline void watchdog_update_worker(struct watchdog_device *wdd) ktime_t t = watchdog_next_keepalive(wdd); if (t > 0) - hrtimer_start(&wd_data->timer, t, HRTIMER_MODE_REL); + hrtimer_start(&wd_data->timer, t, + HRTIMER_MODE_REL_HARD); } else { hrtimer_cancel(&wd_data->timer); } @@ -176,7 +177,7 @@ static int __watchdog_ping(struct watchdog_device *wdd) if (ktime_after(earliest_keepalive, now)) { hrtimer_start(&wd_data->timer, ktime_sub(earliest_keepalive, now), - HRTIMER_MODE_REL); + HRTIMER_MODE_REL_HARD); return 0; } @@ -974,7 +975,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) return -ENODEV; kthread_init_work(&wd_data->work, watchdog_ping_work); - hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD); wd_data->timer.function = watchdog_timer_expired; if (wdd->id == 0) { @@ -1032,7 +1033,8 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) __module_get(wdd->ops->owner); get_device(&wd_data->dev); if (handle_boot_enabled) - hrtimer_start(&wd_data->timer, 0, HRTIMER_MODE_REL); + hrtimer_start(&wd_data->timer, 0, + HRTIMER_MODE_REL_HARD); else pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n", wdd->id); -- cgit v1.2.3