From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> commit d44d26987bb3df6d76556827097fc9ce17565cb8 upstream. Since 135225a363ae timekeeping_cycles_to_ns() handles large offsets which would lead to 64bit multiplication overflows correctly. It's also protected against negative motion of the clocksource unconditionally, which was exclusive to x86 before. timekeeping_advance() handles large offsets already correctly. That means the value of CONFIG_DEBUG_TIMEKEEPING which analyzed these cases is very close to zero. Remove all of it. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Acked-by: John Stultz <jstultz@xxxxxxxxxx> Link: https://lore.kernel.org/all/20241031120328.536010148@xxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/riscv/configs/defconfig | 1 include/linux/timekeeper_internal.h | 15 -- kernel/time/timekeeping.c | 108 -------------------- lib/Kconfig.debug | 13 -- tools/testing/selftests/wireguard/qemu/debug.config | 1 5 files changed, 3 insertions(+), 135 deletions(-) --- a/arch/riscv/configs/defconfig +++ b/arch/riscv/configs/defconfig @@ -301,7 +301,6 @@ CONFIG_DEBUG_MEMORY_INIT=y CONFIG_DEBUG_PER_CPU_MAPS=y CONFIG_SOFTLOCKUP_DETECTOR=y CONFIG_WQ_WATCHDOG=y -CONFIG_DEBUG_TIMEKEEPING=y CONFIG_DEBUG_RT_MUTEXES=y CONFIG_DEBUG_SPINLOCK=y CONFIG_DEBUG_MUTEXES=y --- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h @@ -68,9 +68,6 @@ struct tk_read_base { * shifted nano seconds. * @ntp_error_shift: Shift conversion between clock shifted nano seconds and * ntp shifted nano seconds. - * @last_warning: Warning ratelimiter (DEBUG_TIMEKEEPING) - * @underflow_seen: Underflow warning flag (DEBUG_TIMEKEEPING) - * @overflow_seen: Overflow warning flag (DEBUG_TIMEKEEPING) * * Note: For timespec(64) based interfaces wall_to_monotonic is what * we need to add to xtime (or xtime corrected for sub jiffy times) @@ -124,18 +121,6 @@ struct timekeeper { u32 ntp_err_mult; /* Flag used to avoid updating NTP twice with same second */ u32 skip_second_overflow; -#ifdef CONFIG_DEBUG_TIMEKEEPING - long last_warning; - /* - * These simple flag variables are managed - * without locks, which is racy, but they are - * ok since we don't really care about being - * super precise about how many events were - * seen, just that a problem was observed. - */ - int underflow_seen; - int overflow_seen; -#endif }; #ifdef CONFIG_GENERIC_TIME_VSYSCALL --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -195,97 +195,6 @@ static inline u64 tk_clock_read(const st return clock->read(clock); } -#ifdef CONFIG_DEBUG_TIMEKEEPING -#define WARNING_FREQ (HZ*300) /* 5 minute rate-limiting */ - -static void timekeeping_check_update(struct timekeeper *tk, u64 offset) -{ - - u64 max_cycles = tk->tkr_mono.clock->max_cycles; - const char *name = tk->tkr_mono.clock->name; - - if (offset > max_cycles) { - printk_deferred("WARNING: timekeeping: Cycle offset (%lld) is larger than allowed by the '%s' clock's max_cycles value (%lld): time overflow danger\n", - offset, name, max_cycles); - printk_deferred(" timekeeping: Your kernel is sick, but tries to cope by capping time updates\n"); - } else { - if (offset > (max_cycles >> 1)) { - printk_deferred("INFO: timekeeping: Cycle offset (%lld) is larger than the '%s' clock's 50%% safety margin (%lld)\n", - offset, name, max_cycles >> 1); - printk_deferred(" timekeeping: Your kernel is still fine, but is feeling a bit nervous\n"); - } - } - - if (tk->underflow_seen) { - if (jiffies - tk->last_warning > WARNING_FREQ) { - printk_deferred("WARNING: Underflow in clocksource '%s' observed, time update ignored.\n", name); - printk_deferred(" Please report this, consider using a different clocksource, if possible.\n"); - printk_deferred(" Your kernel is probably still fine.\n"); - tk->last_warning = jiffies; - } - tk->underflow_seen = 0; - } - - if (tk->overflow_seen) { - if (jiffies - tk->last_warning > WARNING_FREQ) { - printk_deferred("WARNING: Overflow in clocksource '%s' observed, time update capped.\n", name); - printk_deferred(" Please report this, consider using a different clocksource, if possible.\n"); - printk_deferred(" Your kernel is probably still fine.\n"); - tk->last_warning = jiffies; - } - tk->overflow_seen = 0; - } -} - -static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles); - -static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr) -{ - struct timekeeper *tk = &tk_core.timekeeper; - u64 now, last, mask, max, delta; - unsigned int seq; - - /* - * Since we're called holding a seqcount, the data may shift - * under us while we're doing the calculation. This can cause - * false positives, since we'd note a problem but throw the - * results away. So nest another seqcount here to atomically - * grab the points we are checking with. - */ - do { - seq = read_seqcount_begin(&tk_core.seq); - now = tk_clock_read(tkr); - last = tkr->cycle_last; - mask = tkr->mask; - max = tkr->clock->max_cycles; - } while (read_seqcount_retry(&tk_core.seq, seq)); - - delta = clocksource_delta(now, last, mask); - - /* - * Try to catch underflows by checking if we are seeing small - * mask-relative negative values. - */ - if (unlikely((~delta & mask) < (mask >> 3))) - tk->underflow_seen = 1; - - /* Check for multiplication overflows */ - if (unlikely(delta > max)) - tk->overflow_seen = 1; - - /* timekeeping_cycles_to_ns() handles both under and overflow */ - return timekeeping_cycles_to_ns(tkr, now); -} -#else -static inline void timekeeping_check_update(struct timekeeper *tk, u64 offset) -{ -} -static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr) -{ - BUG(); -} -#endif - /** * tk_setup_internals - Set up internals to use clocksource clock. * @@ -390,19 +299,11 @@ static inline u64 timekeeping_cycles_to_ return ((delta * tkr->mult) + tkr->xtime_nsec) >> tkr->shift; } -static __always_inline u64 __timekeeping_get_ns(const struct tk_read_base *tkr) +static __always_inline u64 timekeeping_get_ns(const struct tk_read_base *tkr) { return timekeeping_cycles_to_ns(tkr, tk_clock_read(tkr)); } -static inline u64 timekeeping_get_ns(const struct tk_read_base *tkr) -{ - if (IS_ENABLED(CONFIG_DEBUG_TIMEKEEPING)) - return timekeeping_debug_get_ns(tkr); - - return __timekeeping_get_ns(tkr); -} - /** * update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper. * @tkr: Timekeeping readout base from which we take the update @@ -446,7 +347,7 @@ static __always_inline u64 __ktime_get_f seq = raw_read_seqcount_latch(&tkf->seq); tkr = tkf->base + (seq & 0x01); now = ktime_to_ns(tkr->base); - now += __timekeeping_get_ns(tkr); + now += timekeeping_get_ns(tkr); } while (raw_read_seqcount_latch_retry(&tkf->seq, seq)); return now; @@ -562,7 +463,7 @@ static __always_inline u64 __ktime_get_r tkr = tkf->base + (seq & 0x01); basem = ktime_to_ns(tkr->base); baser = ktime_to_ns(tkr->base_real); - delta = __timekeeping_get_ns(tkr); + delta = timekeeping_get_ns(tkr); } while (raw_read_seqcount_latch_retry(&tkf->seq, seq)); if (mono) @@ -2298,9 +2199,6 @@ static bool timekeeping_advance(enum tim if (offset < real_tk->cycle_interval && mode == TK_ADV_TICK) goto out; - /* Do some additional sanity checking */ - timekeeping_check_update(tk, offset); - /* * With NO_HZ we may have to accumulate many cycle_intervals * (think "ticks") worth of time at once. To do this efficiently, --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1328,19 +1328,6 @@ config SCHEDSTATS endmenu -config DEBUG_TIMEKEEPING - bool "Enable extra timekeeping sanity checking" - help - This option will enable additional timekeeping sanity checks - which may be helpful when diagnosing issues where timekeeping - problems are suspected. - - This may include checks in the timekeeping hotpaths, so this - option may have a (very small) performance impact to some - workloads. - - If unsure, say N. - config DEBUG_PREEMPT bool "Debug preemptible kernel" depends on DEBUG_KERNEL && PREEMPTION && TRACE_IRQFLAGS_SUPPORT --- a/tools/testing/selftests/wireguard/qemu/debug.config +++ b/tools/testing/selftests/wireguard/qemu/debug.config @@ -31,7 +31,6 @@ CONFIG_SCHED_DEBUG=y CONFIG_SCHED_INFO=y CONFIG_SCHEDSTATS=y CONFIG_SCHED_STACK_END_CHECK=y -CONFIG_DEBUG_TIMEKEEPING=y CONFIG_DEBUG_PREEMPT=y CONFIG_DEBUG_RT_MUTEXES=y CONFIG_DEBUG_SPINLOCK=y Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are queue-6.12/ntp-remove-invalid-cast-in-time-offset-math.patch queue-6.12/irqchip-stm32mp-exti-config_stm32mp_exti-should-not-.patch queue-6.12/modpost-add-.irqentry.text-to-other_sections.patch queue-6.12/clocksource-make-negative-motion-detection-more-robust.patch queue-6.12/x86-cpu-topology-remove-limit-of-cpus-due-to-disabled-io-apic.patch queue-6.12/timekeeping-remove-config_debug_timekeeping.patch queue-6.12/kvm-x86-mmu-ensure-that-kvm_release_pfn_clean-takes-exact-pfn-from-kvm_faultin_pfn.patch queue-6.12/irqchip-gicv3-its-add-workaround-for-hip09-its-errat.patch queue-6.12/timekeeping-always-check-for-negative-motion.patch
