linux/kernel/time, branch v6.3

Merge tag 'timers-core-2023-02-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2023-02-21T17:45:13Z

Pull timer updates from Thomas Gleixner: "Updates for timekeeping, timers and clockevent/source drivers: Core: - Yet another round of improvements to make the clocksource watchdog more robust: - Relax the clocksource-watchdog skew criteria to match the NTP criteria. - Temporarily skip the watchdog when high memory latencies are detected which can lead to false-positives. - Provide an option to enable TSC skew detection even on systems where TSC is marked as reliable. Sigh! - Initialize the restart block in the nanosleep syscalls to be directed to the no restart function instead of doing a partial setup on entry. This prevents an erroneous restart_syscall() invocation from corrupting user space data. While such a situation is clearly a user space bug, preventing this is a correctness issue and caters to the least suprise principle. - Ignore the hrtimer slack for realtime tasks in schedule_hrtimeout() to align it with the nanosleep semantics. Drivers: - The obligatory new driver bindings for Mediatek, Rockchip and RISC-V variants. - Add support for the C3STOP misfeature to the RISC-V timer to handle the case where the timer stops in deeper idle state. - Set up a static key in the RISC-V timer correctly before first use. - The usual small improvements and fixes all over the place" * tag 'timers-core-2023-02-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits) clocksource/drivers/timer-sun4i: Add CLOCK_EVT_FEAT_DYNIRQ clocksource/drivers/em_sti: Mark driver as non-removable clocksource/drivers/sh_tmu: Mark driver as non-removable clocksource/drivers/riscv: Patch riscv_clock_next_event() jump before first use clocksource/drivers/timer-microchip-pit64b: Add delay timer clocksource/drivers/timer-microchip-pit64b: Select driver only on ARM dt-bindings: timer: sifive,clint: add comaptibles for T-Head's C9xx dt-bindings: timer: mediatek,mtk-timer: add MT8365 clocksource/drivers/riscv: Get rid of clocksource_arch_init() callback clocksource/drivers/sh_cmt: Mark driver as non-removable clocksource/drivers/timer-microchip-pit64b: Drop obsolete dependency on COMPILE_TEST clocksource/drivers/riscv: Increase the clock source rating clocksource/drivers/timer-riscv: Set CLOCK_EVT_FEAT_C3STOP based on DT dt-bindings: timer: Add bindings for the RISC-V timer device RISC-V: time: initialize hrtimer based broadcast clock event device dt-bindings: timer: rk-timer: Add rktimer for rv1126 time/debug: Fix memory leak with using debugfs_lookup() clocksource: Enable TSC watchdog checking of HPET and PMTMR only when requested posix-timers: Use atomic64_try_cmpxchg() in __update_gt_cputime() clocksource: Verify HPET and PMTMR when TSC unverified ...

Merge tag 'sched-core-2023-02-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2023-02-21T01:41:08Z

Pull scheduler updates from Ingo Molnar: - Improve the scalability of the CFS bandwidth unthrottling logic with large number of CPUs. - Fix & rework various cpuidle routines, simplify interaction with the generic scheduler code. Add __cpuidle methods as noinstr to objtool's noinstr detection and fix boatloads of cpuidle bugs & quirks. - Add new ABI: introduce MEMBARRIER_CMD_GET_REGISTRATIONS, to query previously issued registrations. - Limit scheduler slice duration to the sysctl_sched_latency period, to improve scheduling granularity with a large number of SCHED_IDLE tasks. - Debuggability enhancement on sys_exit(): warn about disabled IRQs, but also enable them to prevent a cascade of followup problems and repeat warnings. - Fix the rescheduling logic in prio_changed_dl(). - Micro-optimize cpufreq and sched-util methods. - Micro-optimize ttwu_runnable() - Micro-optimize the idle-scanning in update_numa_stats(), select_idle_capacity() and steal_cookie_task(). - Update the RSEQ code & self-tests - Constify various scheduler methods - Remove unused methods - Refine __init tags - Documentation updates - Misc other cleanups, fixes * tag 'sched-core-2023-02-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (110 commits) sched/rt: pick_next_rt_entity(): check list_entry sched/deadline: Add more reschedule cases to prio_changed_dl() sched/fair: sanitize vruntime of entity being placed sched/fair: Remove capacity inversion detection sched/fair: unlink misfit task from cpu overutilized objtool: mem*() are not uaccess safe cpuidle: Fix poll_idle() noinstr annotation sched/clock: Make local_clock() noinstr sched/clock/x86: Mark sched_clock() noinstr x86/pvclock: Improve atomic update of last_value in pvclock_clocksource_read() x86/atomics: Always inline arch_atomic64*() cpuidle: tracing, preempt: Squash _rcuidle tracing cpuidle: tracing: Warn about !rcu_is_watching() cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG cpuidle: drivers: firmware: psci: Dont instrument suspend code KVM: selftests: Fix build of rseq test exit: Detect and fix irq disabled state in oops cpuidle, arm64: Fix the ARM64 cpuidle logic cpuidle: mvebu: Fix duplicate flags assignment sched/fair: Limit sched slice duration ...

alarmtimer: Prevent starvation by small intervals and SIG_IGN

2023-02-14T10:18:35Z

syzbot reported a RCU stall which is caused by setting up an alarmtimer with a very small interval and ignoring the signal. The reproducer arms the alarm timer with a relative expiry of 8ns and an interval of 9ns. Not a problem per se, but that's an issue when the signal is ignored because then the timer is immediately rearmed because there is no way to delay that rearming to the signal delivery path. See posix_timer_fn() and commit 58229a189942 ("posix-timers: Prevent softirq starvation by small intervals and SIG_IGN") for details. The reproducer does not set SIG_IGN explicitely, but it sets up the timers signal with SIGCONT. That has the same effect as explicitely setting SIG_IGN for a signal as SIGCONT is ignored if there is no handler set and the task is not ptraced. The log clearly shows that: [pid 5102] --- SIGCONT {si_signo=SIGCONT, si_code=SI_TIMER, si_timerid=0, si_overrun=316014, si_int=0, si_ptr=NULL} --- It works because the tasks are traced and therefore the signal is queued so the tracer can see it, which delays the restart of the timer to the signal delivery path. But then the tracer is killed: [pid 5087] kill(-5102, SIGKILL ... ./strace-static-x86_64: Process 5107 detached and after it's gone the stall can be observed: syzkaller login: [ 79.439102][ C0] hrtimer: interrupt took 68471 ns [ 184.460538][ C1] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: ... [ 184.658237][ C1] rcu: Stack dump where RCU GP kthread last ran: [ 184.664574][ C1] Sending NMI from CPU 1 to CPUs 0: [ 184.669821][ C0] NMI backtrace for cpu 0 [ 184.669831][ C0] CPU: 0 PID: 5108 Comm: syz-executor192 Not tainted 6.2.0-rc6-next-20230203-syzkaller #0 ... [ 184.670036][ C0] Call Trace: [ 184.670041][ C0] [ 184.670045][ C0] alarmtimer_fired+0x327/0x670 posix_timer_fn() prevents that by checking whether the interval for timers which have the signal ignored is smaller than a jiffie and artifically delay it by shifting the next expiry out by a jiffie. That's accurate vs. the overrun accounting, but slightly inaccurate vs. timer_gettimer(2). The comment in that function says what needs to be done and there was a fix available for the regular userspace induced SIG_IGN mechanism, but that did not work due to the implicit ignore for SIGCONT and similar signals. This needs to be worked on, but for now the only available workaround is to do exactly what posix_timer_fn() does: Increase the interval of self-rearming timers, which have their signal ignored, to at least a jiffie. Interestingly this has been fixed before via commit ff86bf0c65f1 ("alarmtimer: Rate limit periodic intervals") already, but that fix got lost in a later rework. Reported-by: syzbot+b9564ba6e8e00694511b@syzkaller.appspotmail.com Fixes: f2c45807d399 ("alarmtimer: Switch over to generic set/get/rearm routine") Signed-off-by: Thomas Gleixner Acked-by: John Stultz Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/87k00q1no2.ffs@tglx

Merge tag 'clocksource.2023.02.06b' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into timers/core

2023-02-13T18:28:48Z

Pull clocksource watchdog changes from Paul McKenney: o Improvements to clocksource-watchdog console messages. o Loosening of the clocksource-watchdog skew criteria to match those of NTP (500 parts per million, relaxed from 400 parts per million). If it is good enough for NTP, it is good enough for the clocksource watchdog. o Suspend clocksource-watchdog checking temporarily when high memory latencies are detected. This avoids the false-positive clock-skew events that have been seen on production systems running memory-intensive workloads. o On systems where the TSC is deemed trustworthy, use it as the watchdog timesource, but only when specifically requested using the tsc=watchdog kernel boot parameter. This permits clock-skew events to be detected, but avoids forcing workloads to use the slow HPET and ACPI PM timers. These last two timers are slow enough to cause systems to be needlessly marked bad on the one hand, and real skew does sometimes happen on production systems running production workloads on the other. And sometimes it is the fault of the TSC, or at least of the firmware that told the kernel to program the TSC with the wrong frequency. o Add a tsc=revalidate kernel boot parameter to allow the kernel to diagnose cases where the TSC hardware works fine, but was told by firmware to tick at the wrong frequency. Such cases are rare, but they really have happened on production systems. Link: https://lore.kernel.org/r/20230210193640.GA3325193@paulmck-ThinkPad-P17-Gen-1

time/debug: Fix memory leak with using debugfs_lookup()

2023-02-09T19:12:27Z

When calling debugfs_lookup() the result must have dput() called on it, otherwise the memory will leak over time. To make things simpler, just call debugfs_lookup_and_remove() instead which handles all of the logic at once. Signed-off-by: Greg Kroah-Hartman Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230202151214.2306822-1-gregkh@linuxfoundation.org

posix-timers: Use atomic64_try_cmpxchg() in __update_gt_cputime()

2023-02-06T13:22:09Z

Use atomic64_try_cmpxchg() instead of atomic64_cmpxchg() in __update_gt_cputime(). The x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg() (and related move instruction in front of cmpxchg()). Also, atomic64_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg() fails. There is no need to re-read the value in the loop. No functional change intended. Signed-off-by: Uros Bizjak Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230116165337.5810-1-ubizjak@gmail.com

Merge tag 'v6.2-rc6' into sched/core, to pick up fixes

2023-01-31T14:01:20Z

Pick up fixes before merging another batch of cpuidle updates. Signed-off-by: Ingo Molnar

hrtimer: Ignore slack time for RT tasks in schedule_hrtimeout_range()

2023-01-31T10:23:07Z

While in theory the timer can be triggered before expires + delta, for the cases of RT tasks they really have no business giving any lenience for extra slack time, so override any passed value by the user and always use zero for schedule_hrtimeout_range() calls. Furthermore, this is similar to what the nanosleep(2) family already does with current->timer_slack_ns. Signed-off-by: Davidlohr Bueso Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230123173206.6764-3-dave@stgolabs.net

hrtimer: Rely on rt_task() for DL tasks too

2023-01-31T10:23:07Z

Checking dl_task() is redundant as rt_task() returns true for deadline tasks too. Signed-off-by: Davidlohr Bueso Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230123173206.6764-2-dave@stgolabs.net

clocksource: Suspend the watchdog temporarily when high read latency detected

2023-01-24T23:12:48Z

Bugs have been reported on 8 sockets x86 machines in which the TSC was wrongly disabled when the system is under heavy workload. [ 818.380354] clocksource: timekeeping watchdog on CPU336: hpet wd-wd read-back delay of 1203520ns [ 818.436160] clocksource: wd-tsc-wd read-back delay of 181880ns, clock-skew test skipped! [ 819.402962] clocksource: timekeeping watchdog on CPU338: hpet wd-wd read-back delay of 324000ns [ 819.448036] clocksource: wd-tsc-wd read-back delay of 337240ns, clock-skew test skipped! [ 819.880863] clocksource: timekeeping watchdog on CPU339: hpet read-back delay of 150280ns, attempt 3, marking unstable [ 819.936243] tsc: Marking TSC unstable due to clocksource watchdog [ 820.068173] TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'. [ 820.092382] sched_clock: Marking unstable (818769414384, 1195404998) [ 820.643627] clocksource: Checking clocksource tsc synchronization from CPU 267 to CPUs 0,4,25,70,126,430,557,564. [ 821.067990] clocksource: Switched to clocksource hpet This can be reproduced by running memory intensive 'stream' tests, or some of the stress-ng subcases such as 'ioport'. The reason for these issues is the when system is under heavy load, the read latency of the clocksources can be very high. Even lightweight TSC reads can show high latencies, and latencies are much worse for external clocksources such as HPET or the APIC PM timer. These latencies can result in false-positive clocksource-unstable determinations. These issues were initially reported by a customer running on a production system, and this problem was reproduced on several generations of Xeon servers, especially when running the stress-ng test. These Xeon servers were not production systems, but they did have the latest steppings and firmware. Given that the clocksource watchdog is a continual diagnostic check with frequency of twice a second, there is no need to rush it when the system is under heavy load. Therefore, when high clocksource read latencies are detected, suspend the watchdog timer for 5 minutes. Signed-off-by: Feng Tang Acked-by: Waiman Long Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Feng Tang Signed-off-by: Paul E. McKenney