From: Julia Cartwright <[email protected]> commit e31a286f388949d4098ce0ddb27e2f558eb7fb18 in linux-rt-devel.
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 <[email protected]> Reported-and-tested-by: Steffen Trumtrar <[email protected]> Reported-by: Tim Sander <[email protected]> Signed-off-by: Julia Cartwright <[email protected]> Acked-by: Guenter Roeck <[email protected]> [bigeasy: use only HRTIMER_MODE_REL_HARD] Signed-off-by: Sebastian Andrzej Siewior <[email protected]> Signed-off-by: Paul Gortmaker <[email protected]> --- drivers/watchdog/watchdog_dev.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c index ffbdc4642ea5..84f75b5045f6 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -147,7 +147,7 @@ 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); } @@ -166,7 +166,7 @@ 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; } @@ -945,7 +945,7 @@ 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) { @@ -992,7 +992,7 @@ 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); -- 2.15.0 -- _______________________________________________ linux-yocto mailing list [email protected] https://lists.yoctoproject.org/listinfo/linux-yocto
