linux/kernel/hrtimer.c, branch v3.9

hrtimer: Don't reinitialize a cpu_base lock on CPU_UP

2013-03-26T20:34:57Z

The current code makes the assumption that a cpu_base lock won't be held if the CPU corresponding to that cpu_base is offline, which isn't always true. If a hrtimer is not queued, then it will not be migrated by migrate_hrtimers() when a CPU is offlined. Therefore, the hrtimer's cpu_base may still point to a CPU which has subsequently gone offline if the timer wasn't enqueued at the time the CPU went down. Normally this wouldn't be a problem, but a cpu_base's lock is blindly reinitialized each time a CPU is brought up. If a CPU is brought online during the period that another thread is performing a hrtimer operation on a stale hrtimer, then the lock will be reinitialized under its feet, and a SPIN_BUG() like the following will be observed: <0>[ 28.082085] BUG: spinlock already unlocked on CPU#0, swapper/0/0 <0>[ 28.087078] lock: 0xc4780b40, value 0x0 .magic: dead4ead, .owner: /-1, .owner_cpu: -1 <4>[ 42.451150] [] (unwind_backtrace+0x0/0x120) from [] (do_raw_spin_unlock+0x44/0xdc) <4>[ 42.460430] [] (do_raw_spin_unlock+0x44/0xdc) from [] (_raw_spin_unlock+0x8/0x30) <4>[ 42.469632] [] (_raw_spin_unlock+0x8/0x30) from [] (__hrtimer_start_range_ns+0x1e4/0x4f8) <4>[ 42.479521] [] (__hrtimer_start_range_ns+0x1e4/0x4f8) from [] (hrtimer_start+0x20/0x28) <4>[ 42.489247] [] (hrtimer_start+0x20/0x28) from [] (rcu_idle_enter_common+0x1ac/0x320) <4>[ 42.498709] [] (rcu_idle_enter_common+0x1ac/0x320) from [] (rcu_idle_enter+0xa0/0xb8) <4>[ 42.508259] [] (rcu_idle_enter+0xa0/0xb8) from [] (cpu_idle+0x24/0xf0) <4>[ 42.516503] [] (cpu_idle+0x24/0xf0) from [] (rest_init+0x88/0xa0) <4>[ 42.524319] [] (rest_init+0x88/0xa0) from [] (start_kernel+0x3d0/0x434) As an example, this particular crash occurred when hrtimer_start() was executed on CPU #0. The code locked the hrtimer's current cpu_base corresponding to CPU #1. CPU #0 then tried to switch the hrtimer's cpu_base to an optimal CPU which was online. In this case, it selected the cpu_base corresponding to CPU #3. Before it could proceed, CPU #1 came online and reinitialized the spinlock corresponding to its cpu_base. Thus now CPU #0 held a lock which was reinitialized. When CPU #0 finally ended up unlocking the old cpu_base corresponding to CPU #1 so that it could switch to CPU #3, we hit this SPIN_BUG() above while in switch_hrtimer_base(). CPU #0 CPU #1 ---- ---- ... hrtimer_start() lock_hrtimer_base(base #1) ... init_hrtimers_cpu() switch_hrtimer_base() ... ... raw_spin_lock_init(&cpu_base->lock) raw_spin_unlock(&cpu_base->lock) ... Solve this by statically initializing the lock. Signed-off-by: Michael Bohan Link: http://lkml.kernel.org/r/1363745965-23475-1-git-send-email-mbohan@codeaurora.org Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner

Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2013-02-20T03:05:45Z

Pull timer changes from Ingo Molnar: "Main changes: - ntp: Add CONFIG_RTC_SYSTOHC: a generic RTC driver facility complementing the existing CONFIG_RTC_HCTOSYS, which uses NTP to keep the hardware clock updated. - posix-timers: Fix clock_adjtime to always return timex data on success. This is changing the ABI, but no breakage was expected and found - caution is warranted nevertheless. - platform persistent clock improvements/cleanups. - clockevents: refactor timer broadcast handling to be more generic and less duplicated with matching architecture code (mostly ARM motivated.) - various fixes and cleanups" * 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: timers/x86/hpet: Use HPET_COUNTER to specify the hpet counter in vread_hpet() posix-cpu-timers: Fix nanosleep task_struct leak clockevents: Fix generic broadcast for FEAT_C3STOP time, Fix setting of hardware clock in NTP code hrtimer: Prevent hrtimer_enqueue_reprogram race clockevents: Add generic timer broadcast function clockevents: Add generic timer broadcast receiver timekeeping: Switch HAS_PERSISTENT_CLOCK to ALWAYS_USE_PERSISTENT_CLOCK x86/time/rtc: Don't print extended CMOS year when reading RTC x86: Select HAS_PERSISTENT_CLOCK on x86 timekeeping: Add CONFIG_HAS_PERSISTENT_CLOCK option rtc: Skip the suspend/resume handling if persistent clock exist timekeeping: Add persistent_clock_exist flag posix-timers: Fix clock_adjtime to always return timex data on success Round the calculated scale factor in set_cyc2ns_scale() NTP: Add a CONFIG_RTC_SYSTOHC configuration MAINTAINERS: Update John Stultz's email time: create __getnstimeofday for WARNless calls

sched/rt: Move rt specific bits into new header file

2013-02-07T19:51:08Z

Move rt scheduler definitions out of include/linux/sched.h into new file include/linux/sched/rt.h Signed-off-by: Clark Williams Cc: Peter Zijlstra Cc: Steven Rostedt Link: http://lkml.kernel.org/r/20130207094707.7b9f825f@riff.lan Signed-off-by: Ingo Molnar

sched: Move sched.h sysctl bits into separate header

2013-02-07T19:50:54Z

Move the sysctl-related bits from include/linux/sched.h into a new file: include/linux/sched/sysctl.h. Then update source files requiring access to those bits by including the new header file. Signed-off-by: Clark Williams Cc: Peter Zijlstra Cc: Steven Rostedt Link: http://lkml.kernel.org/r/20130207094659.06dced96@riff.lan Signed-off-by: Ingo Molnar

hrtimer: Prevent hrtimer_enqueue_reprogram race

2013-02-05T10:52:41Z

hrtimer_enqueue_reprogram contains a race which could result in timer.base switch during unlock/lock sequence. hrtimer_enqueue_reprogram is releasing the lock protecting the timer base for calling raise_softirq_irqsoff() due to a lock ordering issue versus rq->lock. If during that time another CPU calls __hrtimer_start_range_ns() on the same hrtimer, the timer base might switch, before the current CPU can lock base->lock again and therefor the unlock_timer_base() call will unlock the wrong lock. [ tglx: Added comment and massaged changelog ] Signed-off-by: Leonid Shatz Signed-off-by: Izik Eidus Cc: Andrea Arcangeli Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1359981217-389-1-git-send-email-izik.eidus@ravellosystems.com Signed-off-by: Thomas Gleixner

hrtimer: Update hrtimer base offsets each hrtimer_interrupt

2012-07-11T21:34:39Z

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

hrtimers: Move lock held region in hrtimer_interrupt()

2012-07-11T21:34:38Z

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

hrtimer: Provide clock_was_set_delayed()

2012-07-11T21:34:37Z

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

Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2011-11-28T16:43:52Z

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: hrtimer: Fix extra wakeups from __remove_hrtimer() timekeeping: add arch_offset hook to ktime_get functions clocksource: Avoid selecting mult values that might overflow when adjusted time: Improve documentation of timekeeeping_adjust()

hrtimer: Fix extra wakeups from __remove_hrtimer()

2011-11-19T11:17:37Z

__remove_hrtimer() attempts to reprogram the clockevent device when the timer being removed is the next to expire. However, __remove_hrtimer() reprograms the clockevent *before* removing the timer from the timerqueue and thus when hrtimer_force_reprogram() finds the next timer to expire it finds the timer we're trying to remove. This is especially noticeable when the system switches to NOHz mode and the system tick is removed. The timer tick is removed from the system but the clockevent is programmed to wakeup in another HZ anyway. Silence the extra wakeup by removing the timer from the timerqueue before calling hrtimer_force_reprogram() so that we actually program the clockevent for the next timer to expire. This was broken by 998adc3 "hrtimers: Convert hrtimers to use timerlist infrastructure". Signed-off-by: Jeff Ohlstein Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1321660030-8520-1-git-send-email-johlstei@codeaurora.org Signed-off-by: Thomas Gleixner