user/sven/linux.git/kernel/time/timer.c, branch v5.13.19

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

2021-08-12T11:32:21Z

commit bb7262b295472eb6858b5c49893954794027cd84 upstream. 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 Signed-off-by: Greg Kroah-Hartman

timers: Fix get_next_timer_interrupt() with no timers pending

2021-07-28T12:37:27Z

[ Upstream commit aebacb7f6ca1926918734faae14d1f0b6fae5cb7 ] 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 Unfortunately, the next expiry time and the timer base clock are no longer updated in unison.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 Signed-off-by: Sasha Levin

timekeeping, clocksource: Fix various typos in comments

2021-03-22T22:06:48Z

Fix ~56 single-word typos in timekeeping & clocksource code comments. Signed-off-by: Ingo Molnar Cc: Thomas Gleixner Cc: John Stultz Cc: Stephen Boyd Cc: Daniel Lezcano Cc: linux-kernel@vger.kernel.org

rcu/nocb: Code-style nits in callback-offloading toggling

2021-01-07T00:47:55Z

This commit addresses a few code-style nits in callback-offloading toggling, including one that predates this toggling. Cc: Frederic Weisbecker Signed-off-by: Paul E. McKenney

timer: Add timer_curr_running()

2021-01-07T00:24:59Z

This commit adds a timer_curr_running() function that verifies that the current code is running in the context of the specified timer's handler. Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay Cc: Thomas Gleixner Tested-by: Boqun Feng Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney

Merge tag 'timers-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-12-15T02:21:14Z

Pull timers and timekeeping updates from Thomas Gleixner: "Core: - Robustness improvements for the NOHZ tick management - Fixes and consolidation of the NTP/RTC synchronization code - Small fixes and improvements in various places - A set of function documentation udpates and fixes Drivers: - Cleanups and improvements in various clocksoure/event drivers - Removal of the EZChip NPS clocksource driver as the platfrom support was removed from ARC - The usual set of new device tree binding and json conversions - The RTC driver which have been acked by the RTC maintainer: * fix a long standing bug in the MC146818 library code which can cause reading garbage during the RTC internal update. * changes related to the NTP/RTC consolidation work" * tag 'timers-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (46 commits) ntp: Fix prototype in the !CONFIG_GENERIC_CMOS_UPDATE case tick/sched: Make jiffies update quick check more robust ntp: Consolidate the RTC update implementation ntp: Make the RTC sync offset less obscure ntp, rtc: Move rtc_set_ntp_time() to ntp code ntp: Make the RTC synchronization more reliable rtc: core: Make the sync offset default more realistic rtc: cmos: Make rtc_cmos sync offset correct rtc: mc146818: Reduce spinlock section in mc146818_set_time() rtc: mc146818: Prevent reading garbage clocksource/drivers/sh_cmt: Fix potential deadlock when calling runtime PM clocksource/drivers/arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI clocksource/drivers/arm_arch_timer: Use stable count reader in erratum sne clocksource/drivers/dw_apb_timer_of: Add error handling if no clock available clocksource/drivers/riscv: Make RISCV_TIMER depends on RISCV_SBI clocksource/drivers/ingenic: Fix section mismatch clocksource/drivers/cadence_ttc: Fix memory leak in ttc_setup_clockevent() dt-bindings: timer: renesas: tmu: Convert to json-schema dt-bindings: timer: renesas: tmu: Document r8a774e1 bindings clocksource/drivers/orion: Add missing clk_disable_unprepare() on error path ...

timers: Make run_local_timers() static

2020-11-16T14:20:01Z

No users outside of the timer code. Move the caller below this function to avoid a pointless forward declaration. Signed-off-by: Thomas Gleixner

timers: Don't block on ->expiry_lock for TIMER_IRQSAFE timers

2020-11-15T19:59:26Z

PREEMPT_RT does not spin and wait until a running timer completes its callback but instead it blocks on a sleeping lock to prevent a livelock in the case that the task waiting for the callback completion preempted the callback. This cannot be done for timers flagged with TIMER_IRQSAFE. These timers can be canceled from an interrupt disabled context even on RT kernels. The expiry callback of such timers is invoked with interrupts disabled so there is no need to use the expiry lock mechanism because obviously the callback cannot be preempted even on RT kernels. Do not use the timer_base::expiry_lock mechanism when waiting for a running callback to complete if the timer is flagged with TIMER_IRQSAFE. Also add a lockdep assertion for RT kernels to validate that the expiry lock mechanism is always invoked in preemptible context. Reported-by: Mike Galbraith Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20201103190937.hga67rqhvknki3tp@linutronix.de

timers: Remove unused inline funtion debug_timer_free()

2020-10-26T10:39:21Z

There is no caller in tree, remove it. Signed-off-by: YueHaibing Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20200909134749.32300-1-yuehaibing@huawei.com

random32: add noise from network and scheduling activity

2020-10-24T18:21:57Z

With the removal of the interrupt perturbations in previous random32 change (random32: make prandom_u32() output unpredictable), the PRNG has become 100% deterministic again. While SipHash is expected to be way more robust against brute force than the previous Tausworthe LFSR, there's still the risk that whoever has even one temporary access to the PRNG's internal state is able to predict all subsequent draws till the next reseed (roughly every minute). This may happen through a side channel attack or any data leak. This patch restores the spirit of commit f227e3ec3b5c ("random32: update the net random state on interrupt and activity") in that it will perturb the internal PRNG's statee using externally collected noise, except that it will not pick that noise from the random pool's bits nor upon interrupt, but will rather combine a few elements along the Tx path that are collectively hard to predict, such as dev, skb and txq pointers, packet length and jiffies values. These ones are combined using a single round of SipHash into a single long variable that is mixed with the net_rand_state upon each invocation. The operation was inlined because it produces very small and efficient code, typically 3 xor, 2 add and 2 rol. The performance was measured to be the same (even very slightly better) than before the switch to SipHash; on a 6-core 12-thread Core i7-8700k equipped with a 40G NIC (i40e), the connection rate dropped from 556k/s to 555k/s while the SYN cookie rate grew from 5.38 Mpps to 5.45 Mpps. Link: https://lore.kernel.org/netdev/20200808152628.GA27941@SDF.ORG/ Cc: George Spelvin Cc: Amit Klein Cc: Eric Dumazet Cc: "Jason A. Donenfeld" Cc: Andy Lutomirski Cc: Kees Cook Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Linus Torvalds Cc: tytso@mit.edu Cc: Florian Westphal Cc: Marc Plumb Tested-by: Sedat Dilek Signed-off-by: Willy Tarreau