From f55a6faa384304c89cfef162768e88374d3312cb Mon Sep 17 00:00:00 2001 From: John Stultz Date: Tue, 10 Jul 2012 18:43:19 -0400 Subject: hrtimer: Provide clock_was_set_delayed() clock_was_set() cannot be called from hard interrupt context because it calls on_each_cpu(). For fixing the widely reported leap seconds issue it is necessary to call it from hard interrupt context, i.e. the timer tick code, which does the timekeeping updates. Provide a new function which denotes it in the hrtimer cpu base structure of the cpu on which it is called and raise the hrtimer softirq. We then execute the clock_was_set() notificiation from softirq context in run_hrtimer_softirq(). The hrtimer softirq is rarely used, so polling the flag there is not a performance issue. [ tglx: Made it depend on CONFIG_HIGH_RES_TIMERS. We really should get rid of all this ifdeffery ASAP ] Signed-off-by: John Stultz Reported-by: Jan Engelhardt Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra Acked-by: Prarit Bhargava Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1341960205-56738-2-git-send-email-johnstul@us.ibm.com Signed-off-by: Thomas Gleixner --- kernel/hrtimer.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'kernel/hrtimer.c') diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index ae34bf51682b..3c24fb2c25c8 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -717,6 +717,19 @@ static int hrtimer_switch_to_hres(void) return 1; } +/* + * Called from timekeeping code to reprogramm the hrtimer interrupt + * device. If called from the timer interrupt context we defer it to + * softirq context. + */ +void clock_was_set_delayed(void) +{ + struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases); + + cpu_base->clock_was_set = 1; + __raise_softirq_irqoff(HRTIMER_SOFTIRQ); +} + #else static inline int hrtimer_hres_active(void) { return 0; } @@ -1395,6 +1408,13 @@ void hrtimer_peek_ahead_timers(void) static void run_hrtimer_softirq(struct softirq_action *h) { + struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases); + + if (cpu_base->clock_was_set) { + cpu_base->clock_was_set = 0; + clock_was_set(); + } + hrtimer_peek_ahead_timers(); } -- cgit v1.2.3 From 196951e91262fccda81147d2bcf7fdab08668b40 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 10 Jul 2012 18:43:23 -0400 Subject: hrtimers: Move lock held region in hrtimer_interrupt() We need to update the base offsets from this code and we need to do that under base->lock. Move the lock held region around the ktime_get() calls. The ktime_get() calls are going to be replaced with a function which gets the time and the offsets atomically. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra Acked-by: Prarit Bhargava Cc: stable@vger.kernel.org Signed-off-by: John Stultz Link: http://lkml.kernel.org/r/1341960205-56738-6-git-send-email-johnstul@us.ibm.com Signed-off-by: Thomas Gleixner --- kernel/hrtimer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'kernel/hrtimer.c') diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 3c24fb2c25c8..8f320af837b5 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -1263,11 +1263,10 @@ void hrtimer_interrupt(struct clock_event_device *dev) cpu_base->nr_events++; dev->next_event.tv64 = KTIME_MAX; + raw_spin_lock(&cpu_base->lock); entry_time = now = ktime_get(); retry: expires_next.tv64 = KTIME_MAX; - - raw_spin_lock(&cpu_base->lock); /* * We set expires_next to KTIME_MAX here with cpu_base->lock * held to prevent that a timer is enqueued in our queue via @@ -1344,6 +1343,7 @@ retry: * interrupt routine. We give it 3 attempts to avoid * overreacting on some spurious event. */ + raw_spin_lock(&cpu_base->lock); now = ktime_get(); cpu_base->nr_retries++; if (++retries < 3) @@ -1356,6 +1356,7 @@ retry: */ cpu_base->nr_hangs++; cpu_base->hang_detected = 1; + raw_spin_unlock(&cpu_base->lock); delta = ktime_sub(now, entry_time); if (delta.tv64 > cpu_base->max_hang_time.tv64) cpu_base->max_hang_time = delta; -- cgit v1.2.3 From 5baefd6d84163443215f4a99f6a20f054ef11236 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Tue, 10 Jul 2012 18:43:25 -0400 Subject: hrtimer: Update hrtimer base offsets each hrtimer_interrupt The update of the hrtimer base offsets on all cpus cannot be made atomically from the timekeeper.lock held and interrupt disabled region as smp function calls are not allowed there. clock_was_set(), which enforces the update on all cpus, is called either from preemptible process context in case of do_settimeofday() or from the softirq context when the offset modification happened in the timer interrupt itself due to a leap second. In both cases there is a race window for an hrtimer interrupt between dropping timekeeper lock, enabling interrupts and clock_was_set() issuing the updates. Any interrupt which arrives in that window will see the new time but operate on stale offsets. So we need to make sure that an hrtimer interrupt always sees a consistent state of time and offsets. ktime_get_update_offsets() allows us to get the current monotonic time and update the per cpu hrtimer base offsets from hrtimer_interrupt() to capture a consistent state of monotonic time and the offsets. The function replaces the existing ktime_get() calls in hrtimer_interrupt(). The overhead of the new function vs. ktime_get() is minimal as it just adds two store operations. This ensures that any changes to realtime or boottime offsets are noticed and stored into the per-cpu hrtimer base structures, prior to any hrtimer expiration and guarantees that timers are not expired early. Signed-off-by: John Stultz Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra Acked-by: Prarit Bhargava Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1341960205-56738-8-git-send-email-johnstul@us.ibm.com Signed-off-by: Thomas Gleixner --- kernel/hrtimer.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) (limited to 'kernel/hrtimer.c') diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 8f320af837b5..6db7a5ed52b5 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -657,6 +657,14 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, return 0; } +static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base) +{ + ktime_t *offs_real = &base->clock_base[HRTIMER_BASE_REALTIME].offset; + ktime_t *offs_boot = &base->clock_base[HRTIMER_BASE_BOOTTIME].offset; + + return ktime_get_update_offsets(offs_real, offs_boot); +} + /* * Retrigger next event is called after clock was set * @@ -665,22 +673,12 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, static void retrigger_next_event(void *arg) { struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases); - struct timespec realtime_offset, xtim, wtm, sleep; if (!hrtimer_hres_active()) return; - /* Optimized out for !HIGH_RES */ - get_xtime_and_monotonic_and_sleep_offset(&xtim, &wtm, &sleep); - set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec); - - /* Adjust CLOCK_REALTIME offset */ raw_spin_lock(&base->lock); - base->clock_base[HRTIMER_BASE_REALTIME].offset = - timespec_to_ktime(realtime_offset); - base->clock_base[HRTIMER_BASE_BOOTTIME].offset = - timespec_to_ktime(sleep); - + hrtimer_update_base(base); hrtimer_force_reprogram(base, 0); raw_spin_unlock(&base->lock); } @@ -710,7 +708,6 @@ static int hrtimer_switch_to_hres(void) base->clock_base[i].resolution = KTIME_HIGH_RES; tick_setup_sched_timer(); - /* "Retrigger" the interrupt to get things going */ retrigger_next_event(NULL); local_irq_restore(flags); @@ -1264,7 +1261,7 @@ void hrtimer_interrupt(struct clock_event_device *dev) dev->next_event.tv64 = KTIME_MAX; raw_spin_lock(&cpu_base->lock); - entry_time = now = ktime_get(); + entry_time = now = hrtimer_update_base(cpu_base); retry: expires_next.tv64 = KTIME_MAX; /* @@ -1342,9 +1339,12 @@ retry: * We need to prevent that we loop forever in the hrtimer * interrupt routine. We give it 3 attempts to avoid * overreacting on some spurious event. + * + * Acquire base lock for updating the offsets and retrieving + * the current time. */ raw_spin_lock(&cpu_base->lock); - now = ktime_get(); + now = hrtimer_update_base(cpu_base); cpu_base->nr_retries++; if (++retries < 3) goto retry; -- cgit v1.2.3