linux/kernel/time, branch v5.14

timers: Move clearing of base::timer_running under base:: Lock

2021-07-27T18:57:44Z

syzbot reported KCSAN data races vs. timer_base::timer_running being set to NULL without holding base::lock in expire_timers(). This looks innocent and most reads are clearly not problematic, but Frederic identified an issue which is: int data = 0; void timer_func(struct timer_list *t) { data = 1; } CPU 0 CPU 1 ------------------------------ -------------------------- base = lock_timer_base(timer, &flags); raw_spin_unlock(&base->lock); if (base->running_timer != timer) call_timer_fn(timer, fn, baseclk); ret = detach_if_pending(timer, base, true); base->running_timer = NULL; raw_spin_unlock_irqrestore(&base->lock, flags); raw_spin_lock(&base->lock); x = data; If the timer has previously executed on CPU 1 and then CPU 0 can observe base->running_timer == NULL and returns, assuming the timer has completed, but it's not guaranteed on all architectures. The comment for del_timer_sync() makes that guarantee. Moving the assignment under base->lock prevents this. For non-RT kernel it's performance wise completely irrelevant whether the store happens before or after taking the lock. For an RT kernel moving the store under the lock requires an extra unlock/lock pair in the case that there is a waiter for the timer, but that's not the end of the world. Reported-by: syzbot+aa7c2385d46c5eba0b89@syzkaller.appspotmail.com Reported-by: syzbot+abea4558531bae1ba9fe@syzkaller.appspotmail.com Fixes: 030dcdd197d7 ("timers: Prepare support for PREEMPT_RT") Signed-off-by: Thomas Gleixner Tested-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/87lfea7gw8.fsf@nanos.tec.linutronix.de Cc: stable@vger.kernel.org

timers: Fix get_next_timer_interrupt() with no timers pending

2021-07-14T23:23:54Z

31cd0e119d50 ("timers: Recalculate next timer interrupt only when necessary") subtly altered get_next_timer_interrupt()'s behaviour. The function no longer consistently returns KTIME_MAX with no timers pending. In order to decide if there are any timers pending we check whether the next expiry will happen NEXT_TIMER_MAX_DELTA jiffies from now. Unfortunately, the next expiry time and the timer base clock are no longer updated in unison. The former changes upon certain timer operations (enqueue, expire, detach), whereas the latter keeps track of jiffies as they move forward. Ultimately breaking the logic above. A simplified example: - Upon entering get_next_timer_interrupt() with: jiffies = 1 base->clk = 0; base->next_expiry = NEXT_TIMER_MAX_DELTA; 'base->next_expiry == base->clk + NEXT_TIMER_MAX_DELTA', the function returns KTIME_MAX. - 'base->clk' is updated to the jiffies value. - The next time we enter get_next_timer_interrupt(), taking into account no timer operations happened: base->clk = 1; base->next_expiry = NEXT_TIMER_MAX_DELTA; 'base->next_expiry != base->clk + NEXT_TIMER_MAX_DELTA', the function returns a valid expire time, which is incorrect. This ultimately might unnecessarily rearm sched's timer on nohz_full setups, and add latency to the system[1]. So, introduce 'base->timers_pending'[2], update it every time 'base->next_expiry' changes, and use it in get_next_timer_interrupt(). [1] See tick_nohz_stop_tick(). [2] A quick pahole check on x86_64 and arm64 shows it doesn't make 'struct timer_base' any bigger. Fixes: 31cd0e119d50 ("timers: Recalculate next timer interrupt only when necessary") Signed-off-by: Nicolas Saenz Julienne Signed-off-by: Frederic Weisbecker

posix-cpu-timers: Fix rearm racing against process tick

2021-07-14T23:20:10Z

Since the process wide cputime counter is started locklessly from posix_cpu_timer_rearm(), it can be concurrently stopped by operations on other timers from the same thread group, such as in the following unlucky scenario: CPU 0 CPU 1 ----- ----- timer_settime(TIMER B) posix_cpu_timer_rearm(TIMER A) cpu_clock_sample_group() (pct->timers_active already true) handle_posix_cpu_timers() check_process_timers() stop_process_timers() pct->timers_active = false arm_timer(TIMER A) tick -> run_posix_cpu_timers() // sees !pct->timers_active, ignore // our TIMER A Fix this with simply locking process wide cputime counting start and timer arm in the same block. Acked-by: Peter Zijlstra (Intel) Signed-off-by: Frederic Weisbecker Fixes: 60f2ceaa8111 ("posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group") Cc: stable@vger.kernel.org Cc: Oleg Nesterov Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Eric W. Biederman

Merge branch 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

2021-07-04T19:58:33Z

Pull RCU updates from Paul McKenney: - Bitmap parsing support for "all" as an alias for all bits - Documentation updates - Miscellaneous fixes, including some that overlap into mm and lockdep - kvfree_rcu() updates - mem_dump_obj() updates, with acks from one of the slab-allocator maintainers - RCU NOCB CPU updates, including limited deoffloading - SRCU updates - Tasks-RCU updates - Torture-test updates * 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits) tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states rcu: Add missing __releases() annotation rcu: Remove obsolete rcu_read_unlock() deadlock commentary rcu: Improve comments describing RCU read-side critical sections rcu: Create an unrcu_pointer() to remove __rcu from a pointer srcu: Early test SRCU polling start rcu: Fix various typos in comments rcu/nocb: Unify timers rcu/nocb: Prepare for fine-grained deferred wakeup rcu/nocb: Only cancel nocb timer if not polling rcu/nocb: Delete bypass_timer upon nocb_gp wakeup rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup rcu/nocb: Allow de-offloading rdp leader rcu/nocb: Directly call __wake_nocb_gp() from bypass timer rcu: Don't penalize priority boosting when there is nothing to boost rcu: Point to documentation of ordering guarantees rcu: Make rcu_gp_cleanup() be noinline for tracing rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP ...

Merge tag 'timers-core-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-29T19:31:16Z

Pull timer updates from Thomas Gleixner: "Time and clocksource/clockevent related updates: Core changes: - Infrastructure to support per CPU "broadcast" devices for per CPU clockevent devices which stop in deep idle states. This allows us to utilize the more efficient architected timer on certain ARM SoCs for normal operation instead of permanentely using the slow to access SoC specific clockevent device. - Print the name of the broadcast/wakeup device in /proc/timer_list - Make the clocksource watchdog more robust against delays between reading the current active clocksource and the watchdog clocksource. Such delays can be caused by NMIs, SMIs and vCPU preemption. Handle this by reading the watchdog clocksource twice, i.e. before and after reading the current active clocksource. In case that the two watchdog reads shows an excessive time delta, the read sequence is repeated up to 3 times. - Improve the debug output and add a test module for the watchdog mechanism. - Reimplementation of the venerable time64_to_tm() function with a faster and significantly smaller version. Straight from the source, i.e. the author of the related research paper contributed this! Driver changes: - No new drivers, not even new device tree bindings! - Fixes, improvements and cleanups and all over the place" * tag 'timers-core-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits) time/kunit: Add missing MODULE_LICENSE() time: Improve performance of time64_to_tm() clockevents: Use list_move() instead of list_del()/list_add() clocksource: Print deviation in nanoseconds when a clocksource becomes unstable clocksource: Provide kernel module to test clocksource watchdog clocksource: Reduce clocksource-skew threshold clocksource: Limit number of CPUs checked for clock synchronization clocksource: Check per-CPU clock synchronization when marked unstable clocksource: Retry clock read if long delays detected clockevents: Add missing parameter documentation clocksource/drivers/timer-ti-dm: Drop unnecessary restore clocksource/arm_arch_timer: Improve Allwinner A64 timer workaround clocksource/drivers/arm_global_timer: Remove duplicated argument in arm_global_timer clocksource/drivers/arm_global_timer: Make symbol 'gt_clk_rate_change_nb' static arm: zynq: don't disable CONFIG_ARM_GLOBAL_TIMER due to CONFIG_CPU_FREQ anymore clocksource/drivers/arm_global_timer: Implement rate compensation whenever source clock changes clocksource/drivers/ingenic: Rename unreasonable array names clocksource/drivers/timer-ti-dm: Save and restore timer TIOCP_CFG clocksource/drivers/mediatek: Ack and disable interrupts on suspend clocksource/drivers/samsung_pwm: Constify source IO memory ...

Merge tag 'timers-nohz-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-28T19:22:06Z

Pull timers/nohz updates from Ingo Molnar: - Micro-optimize tick_nohz_full_cpu() - Optimize idle exit tick restarts to be less eager - Optimize tick_nohz_dep_set_task() to only wake up a single CPU. This reduces IPIs and interruptions on nohz_full CPUs. - Optimize tick_nohz_dep_set_signal() in a similar fashion. - Skip IPIs in tick_nohz_kick_task() when trying to kick a non-running task. - Micro-optimize tick_nohz_task_switch() IRQ flags handling to reduce context switching costs. - Misc cleanups and fixes * tag 'timers-nohz-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: MAINTAINERS: Add myself as context tracking maintainer tick/nohz: Call tick_nohz_task_switch() with interrupts disabled tick/nohz: Kick only _queued_ task whose tick dependency is updated tick/nohz: Change signal tick dependency to wake up CPUs of member tasks tick/nohz: Only wake up a single target cpu when kicking a task tick/nohz: Update nohz_full Kconfig help tick/nohz: Update idle_exittime on actual idle exit tick/nohz: Remove superflous check for CONFIG_VIRT_CPU_ACCOUNTING_NATIVE tick/nohz: Conditionally restart tick on idle exit tick/nohz: Evaluate the CPU expression after the static key

time/kunit: Add missing MODULE_LICENSE()

2021-06-28T05:40:23Z

[ mingo: MODULE_LICENSE() takes a string. ] Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar

time: Improve performance of time64_to_tm()

2021-06-24T09:51:59Z

The current implementation of time64_to_tm() contains unnecessary loops, branches and look-up tables. The new one uses an arithmetic-based algorithm appeared in [1] and is approximately 3x faster (YMMV). The drawback is that the new code isn't intuitive and contains many 'magic numbers' (not unusual for this type of algorithm). However, [1] justifies all those numbers and, given this function's history, the code is unlikely to need much maintenance, if any at all. Add a KUnit test for it which checks every day in a 160,000 years interval centered at 1970-01-01 against the expected result. [1] Neri, Schneider, "Euclidean Affine Functions and Applications to Calendar Algorithms". https://arxiv.org/abs/2102.06959 Signed-off-by: Cassio Neri Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210622213616.313046-1-cassio.neri@gmail.com

clockevents: Use list_move() instead of list_del()/list_add()

2021-06-22T15:16:46Z

Simplify the code. Reported-by: Hulk Robot Signed-off-by: Baokun Li Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210609070242.1322450-1-libaokun1@huawei.com

clocksource: Print deviation in nanoseconds when a clocksource becomes unstable

2021-06-22T14:53:17Z

Currently when an unstable clocksource is detected, the raw counters of that clocksource and watchdog will be printed, which can only be understood after some math calculation. So print the delta in nanoseconds as well to make it easier for humans to check the results. [ paulmck: Fix typo. ] Signed-off-by: Feng Tang Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210527190124.440372-6-paulmck@kernel.org