From: Julia Cartwright <julia@xxxxxx> [ Upstream commit a19f89335f4bda3d77d991c96583e3e51856acbb ] 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@xxxxxx Cc: Guenter Roeck <linux@xxxxxxxxxxxx> Reported-and-tested-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> Reported-by: Tim Sander <tim@xxxxxxxxxxxxxxx> Signed-off-by: Julia Cartwright <julia@xxxxxx> Acked-by: Guenter Roeck <linux@xxxxxxxxxxxx> [bigeasy: use only HRTIMER_MODE_REL_HARD] Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20191105144506.clyadjbvnn7b7b2m@xxxxxxxxxxxxx Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> Signed-off-by: Wim Van Sebroeck <wim@xxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 dbd2ad4c9294..d3acc0a7256c 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -158,7 +158,8 @@ 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); } @@ -177,7 +178,7 @@ 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; } @@ -971,7 +972,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno) 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) { @@ -1019,7 +1020,8 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno) __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); -- 2.20.1
