From: Julia Cartwright Date: Fri, 28 Sep 2018 21:03:51 +0000 Subject: [PATCH] watchdog: prevent deferral of watchdogd wakeup on RT Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.25-rt16.tar.xz When PREEMPT_RT_FULL is enabled, all hrtimer expiry functions are deferred for execution into the context of ktimersoftd 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 ktimersoftd also means that for correct behavior a user must adjust the scheduling parameters of both watchdogd _and_ ktimersoftd, 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. 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 --- drivers/watchdog/watchdog_dev.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -147,7 +147,7 @@ static inline void watchdog_update_worke 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); } @@ -166,7 +166,7 @@ static int __watchdog_ping(struct watchd 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; } @@ -945,7 +945,7 @@ static int watchdog_cdev_register(struct 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) { @@ -992,7 +992,7 @@ static int watchdog_cdev_register(struct __module_get(wdd->ops->owner); kref_get(&wd_data->kref); 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);