Pull more timer updates from Thomas Gleixner:
"Timekeeping and clocksource/event driver updates the second batch:
- A trivial documentation fix in the timekeeping core
- A really boring set of small fixes, enhancements and cleanups in
the drivers code. No new clocksource/clockevent drivers for a
change"
* tag 'timers-core-2023-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timekeeping: Fix references to nonexistent ktime_get_fast_ns()
dt-bindings: timer: rockchip: Add rk3588 compatible
dt-bindings: timer: rockchip: Drop superfluous rk3288 compatible
clocksource/drivers/ti: Use of_property_read_bool() for boolean properties
clocksource/drivers/timer-ti-dm: Fix finding alwon timer
clocksource/drivers/davinci: Fix memory leak in davinci_timer_register when init fails
clocksource/drivers/stm32-lp: Drop of_match_ptr for ID table
clocksource/drivers/timer-ti-dm: Convert to platform remove callback returning void
clocksource/drivers/timer-tegra186: Convert to platform remove callback returning void
clocksource/drivers/timer-ti-dm: Improve error message in .remove
clocksource/drivers/timer-stm32-lp: Mark driver as non-removable
clocksource/drivers/sh_mtu2: Mark driver as non-removable
clocksource/drivers/timer-ti-dm: Use of_address_to_resource()
clocksource/drivers/timer-imx-gpt: Remove non-DT function
clocksource/drivers/timer-mediatek: Split out CPUXGPT timers
clocksource/drivers/exynos_mct: Explicitly return 0 for shared timer
Pull driver core updates from Greg KH:
"Here is the large set of driver core changes for 6.4-rc1.
Once again, a busy development cycle, with lots of changes happening
in the driver core in the quest to be able to move "struct bus" and
"struct class" into read-only memory, a task now complete with these
changes.
This will make the future rust interactions with the driver core more
"provably correct" as well as providing more obvious lifetime rules
for all busses and classes in the kernel.
The changes required for this did touch many individual classes and
busses as many callbacks were changed to take const * parameters
instead. All of these changes have been submitted to the various
subsystem maintainers, giving them plenty of time to review, and most
of them actually did so.
Other than those changes, included in here are a small set of other
things:
- kobject logging improvements
- cacheinfo improvements and updates
- obligatory fw_devlink updates and fixes
- documentation updates
- device property cleanups and const * changes
- firwmare loader dependency fixes.
All of these have been in linux-next for a while with no reported
problems"
* tag 'driver-core-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (120 commits)
device property: make device_property functions take const device *
driver core: update comments in device_rename()
driver core: Don't require dynamic_debug for initcall_debug probe timing
firmware_loader: rework crypto dependencies
firmware_loader: Strip off \n from customized path
zram: fix up permission for the hot_add sysfs file
cacheinfo: Add use_arch[|_cache]_info field/function
arch_topology: Remove early cacheinfo error message if -ENOENT
cacheinfo: Check cache properties are present in DT
cacheinfo: Check sib_leaf in cache_leaves_are_shared()
cacheinfo: Allow early level detection when DT/ACPI info is missing/broken
cacheinfo: Add arm64 early level initializer implementation
cacheinfo: Add arch specific early level initializer
tty: make tty_class a static const structure
driver core: class: remove struct class_interface * from callbacks
driver core: class: mark the struct class in struct class_interface constant
driver core: class: make class_register() take a const *
driver core: class: mark class_release() as taking a const *
driver core: remove incorrect comment for device_create*
MIPS: vpe-cmp: remove module owner pointer from struct class usage.
...
Pull timers and timekeeping updates from Thomas Gleixner:
- Improve the VDSO build time checks to cover all dynamic relocations
VDSO does not allow dynamic relocations, but the build time check is
incomplete and fragile.
It's based on architectures specifying the relocation types to search
for and does not handle R_*_NONE relocation entries correctly.
R_*_NONE relocations are injected by some GNU ld variants if they
fail to determine the exact .rel[a]/dyn_size to cover trailing zeros.
R_*_NONE relocations must be ignored by dynamic loaders, so they
should be ignored in the build time check too.
Remove the architecture specific relocation types to check for and
validate strictly that no other relocations than R_*_NONE end up in
the VSDO .so file.
- Prefer signal delivery to the current thread for
CLOCK_PROCESS_CPUTIME_ID based posix-timers
Such timers prefer to deliver the signal to the main thread of a
process even if the context in which the timer expires is the current
task. This has the downside that it might wake up an idle thread.
As there is no requirement or guarantee that the signal has to be
delivered to the main thread, avoid this by preferring the current
task if it is part of the thread group which shares sighand.
This not only avoids waking idle threads, it also distributes the
signal delivery in case of multiple timers firing in the context of
different threads close to each other better.
- Align the tick period properly (again)
For a long time the tick was starting at CLOCK_MONOTONIC zero, which
allowed users space applications to either align with the tick or to
place a periodic computation so that it does not interfere with the
tick. The alignement of the tick period was more by chance than by
intention as the tick is set up before a high resolution clocksource
is installed, i.e. timekeeping is still tick based and the tick
period advances from there.
The early enablement of sched_clock() broke this alignement as the
time accumulated by sched_clock() is taken into account when
timekeeping is initialized. So the base value now(CLOCK_MONOTONIC) is
not longer a multiple of tick periods, which breaks applications
which relied on that behaviour.
Cure this by aligning the tick starting point to the next multiple of
tick periods, i.e 1000ms/CONFIG_HZ.
- A set of NOHZ fixes and enhancements:
* Cure the concurrent writer race for idle and IO sleeptime
statistics
The statitic values which are exposed via /proc/stat are updated
from the CPU local idle exit and remotely by cpufreq, but that
happens without any form of serialization. As a consequence
sleeptimes can be accounted twice or worse.
Prevent this by restricting the accumulation writeback to the CPU
local idle exit and let the remote access compute the accumulated
value.
* Protect idle/iowait sleep time with a sequence count
Reading idle/iowait sleep time, e.g. from /proc/stat, can race
with idle exit updates. As a consequence the readout may result
in random and potentially going backwards values.
Protect this by a sequence count, which fixes the idle time
statistics issue, but cannot fix the iowait time problem because
iowait time accounting races with remote wake ups decrementing
the remote runqueues nr_iowait counter. The latter is impossible
to fix, so the only way to deal with that is to document it
properly and to remove the assertion in the selftest which
triggers occasionally due to that.
* Restructure struct tick_sched for better cache layout
* Some small cleanups and a better cache layout for struct
tick_sched
- Implement the missing timer_wait_running() callback for POSIX CPU
timers
For unknown reason the introduction of the timer_wait_running()
callback missed to fixup posix CPU timers, which went unnoticed for
almost four years.
While initially only targeted to prevent livelocks between a timer
deletion and the timer expiry function on PREEMPT_RT enabled kernels,
it turned out that fixing this for mainline is not as trivial as just
implementing a stub similar to the hrtimer/timer callbacks.
The reason is that for CONFIG_POSIX_CPU_TIMERS_TASK_WORK enabled
systems there is a livelock issue independent of RT.
CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y moves the expiry of POSIX CPU
timers out from hard interrupt context to task work, which is handled
before returning to user space or to a VM. The expiry mechanism moves
the expired timers to a stack local list head with sighand lock held.
Once sighand is dropped the task can be preempted and a task which
wants to delete a timer will spin-wait until the expiry task is
scheduled back in. In the worst case this will end up in a livelock
when the preempting task and the expiry task are pinned on the same
CPU.
The timer wheel has a timer_wait_running() mechanism for RT, which
uses a per CPU timer-base expiry lock which is held by the expiry
code and the task waiting for the timer function to complete blocks
on that lock.
This does not work in the same way for posix CPU timers as there is
no timer base and expiry for process wide timers can run on any task
belonging to that process, but the concept of waiting on an expiry
lock can be used too in a slightly different way.
Add a per task mutex to struct posix_cputimers_work, let the expiry
task hold it accross the expiry function and let the deleting task
which waits for the expiry to complete block on the mutex.
In the non-contended case this results in an extra
mutex_lock()/unlock() pair on both sides.
This avoids spin-waiting on a task which is scheduled out, prevents
the livelock and cures the problem for RT and !RT systems
* tag 'timers-core-2023-04-24' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
posix-cpu-timers: Implement the missing timer_wait_running callback
selftests/proc: Assert clock_gettime(CLOCK_BOOTTIME) VS /proc/uptime monotonicity
selftests/proc: Remove idle time monotonicity assertions
MAINTAINERS: Remove stale email address
timers/nohz: Remove middle-function __tick_nohz_idle_stop_tick()
timers/nohz: Add a comment about broken iowait counter update race
timers/nohz: Protect idle/iowait sleep time under seqcount
timers/nohz: Only ever update sleeptime from idle exit
timers/nohz: Restructure and reshuffle struct tick_sched
tick/common: Align tick period with the HZ tick.
selftests/timers/posix_timers: Test delivery of signals across threads
posix-timers: Prefer delivery of signals to the current thread
vdso: Improve cmd_vdso_check to check all dynamic relocations
For some unknown reason the introduction of the timer_wait_running callback
missed to fixup posix CPU timers, which went unnoticed for almost four years.
Marco reported recently that the WARN_ON() in timer_wait_running()
triggers with a posix CPU timer test case.
Posix CPU timers have two execution models for expiring timers depending on
CONFIG_POSIX_CPU_TIMERS_TASK_WORK:
1) If not enabled, the expiry happens in hard interrupt context so
spin waiting on the remote CPU is reasonably time bound.
Implement an empty stub function for that case.
2) If enabled, the expiry happens in task work before returning to user
space or guest mode. The expired timers are marked as firing and moved
from the timer queue to a local list head with sighand lock held. Once
the timers are moved, sighand lock is dropped and the expiry happens in
fully preemptible context. That means the expiring task can be scheduled
out, migrated, interrupted etc. So spin waiting on it is more than
suboptimal.
The timer wheel has a timer_wait_running() mechanism for RT, which uses
a per CPU timer-base expiry lock which is held by the expiry code and the
task waiting for the timer function to complete blocks on that lock.
This does not work in the same way for posix CPU timers as there is no
timer base and expiry for process wide timers can run on any task
belonging to that process, but the concept of waiting on an expiry lock
can be used too in a slightly different way:
- Add a mutex to struct posix_cputimers_work. This struct is per task
and used to schedule the expiry task work from the timer interrupt.
- Add a task_struct pointer to struct cpu_timer which is used to store
a the task which runs the expiry. That's filled in when the task
moves the expired timers to the local expiry list. That's not
affecting the size of the k_itimer union as there are bigger union
members already
- Let the task take the expiry mutex around the expiry function
- Let the waiter acquire a task reference with rcu_read_lock() held and
block on the expiry mutex
This avoids spin-waiting on a task which might not even be on a CPU and
works nicely for RT too.
Fixes: ec8f954a40 ("posix-timers: Use a callback for cancel synchronization on PREEMPT_RT")
Reported-by: Marco Elver <elver@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marco Elver <elver@google.com>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87zg764ojw.ffs@tglx
The per-cpu iowait task counter is incremented locally upon sleeping.
But since the task can be woken to (and by) another CPU, the counter may
then be decremented remotely. This is the source of a race involving
readers VS writer of idle/iowait sleeptime.
The following scenario shows an example where a /proc/stat reader
observes a pending sleep time as IO whereas that pending sleep time
later eventually gets accounted as non-IO.
CPU 0 CPU 1 CPU 2
----- ----- ------
//io_schedule() TASK A
current->in_iowait = 1
rq(0)->nr_iowait++
//switch to idle
// READ /proc/stat
// See nr_iowait_cpu(0) == 1
return ts->iowait_sleeptime +
ktime_sub(ktime_get(), ts->idle_entrytime)
//try_to_wake_up(TASK A)
rq(0)->nr_iowait--
//idle exit
// See nr_iowait_cpu(0) == 0
ts->idle_sleeptime += ktime_sub(ktime_get(), ts->idle_entrytime)
As a result subsequent reads on /proc/stat may expose backward progress.
This is unfortunately hardly fixable. Just add a comment about that
condition.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-5-frederic@kernel.org
Reading idle/IO sleep time (eg: from /proc/stat) can race with idle exit
updates because the state machine handling the stats is not atomic and
requires a coherent read batch.
As a result reading the sleep time may report irrelevant or backward
values.
Fix this with protecting the simple state machine within a seqcount.
This is expected to be cheap enough not to add measurable performance
impact on the idle path.
Note this only fixes reader VS writer condition partitially. A race
remains that involves remote updates of the CPU iowait task counter. It
can hardly be fixed.
Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-4-frederic@kernel.org
The idle and IO sleeptime statistics appearing in /proc/stat can be
currently updated from two sites: locally on idle exit and remotely
by cpufreq. However there is no synchronization mechanism protecting
concurrent updates. It is therefore possible to account the sleeptime
twice, among all the other possible broken scenarios.
To prevent from breaking the sleeptime accounting source, restrict the
sleeptime updates to the local idle exit site. If there is a delta to
add since the last update, IO/Idle sleep time readers will now only
compute the delta without actually writing it back to the internal idle
statistic fields.
This fixes a writer VS writer race. Note there are still two known
reader VS writer races to handle. A subsequent patch will fix one.
Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-3-frederic@kernel.org
With HIGHRES enabled tick_sched_timer() is programmed every jiffy to
expire the timer_list timers. This timer is programmed accurate in
respect to CLOCK_MONOTONIC so that 0 seconds and nanoseconds is the
first tick and the next one is 1000/CONFIG_HZ ms later. For HZ=250 it is
every 4 ms and so based on the current time the next tick can be
computed.
This accuracy broke since the commit mentioned below because the jiffy
based clocksource is initialized with higher accuracy in
read_persistent_wall_and_boot_offset(). This higher accuracy is
inherited during the setup in tick_setup_device(). The timer still fires
every 4ms with HZ=250 but timer is no longer aligned with
CLOCK_MONOTONIC with 0 as it origin but has an offset in the us/ns part
of the timestamp. The offset differs with every boot and makes it
impossible for user land to align with the tick.
Align the tick period with CLOCK_MONOTONIC ensuring that it is always a
multiple of 1000/CONFIG_HZ ms.
Fixes: 857baa87b6 ("sched/clock: Enable sched clock early")
Reported-by: Gusenleitner Klaus <gus@keba.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/20230406095735.0_14edn3@linutronix.de
Link: https://lore.kernel.org/r/20230418122639.ikgfvu3f@linutronix.de
For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
torture tests that do offlining to end up trying to offline this CPU causing
test failures. Such failure happens on all architectures.
Fix the repeated error messages thrown by this (even if the hotplug errors are
harmless) by asking the opinion of the nohz subsystem on whether the CPU can be
hotplugged.
[ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ]
For drivers/base/ portion:
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Zhouyi Zhou <zhouzhouyi@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: rcu <rcu@vger.kernel.org>
Cc: stable@vger.kernel.org
Fixes: 2987557f52 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
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
...
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
...
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
58229a1899 ("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 <unfinished ...>
...
./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] <IRQ>
[ 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 ff86bf0c65
("alarmtimer: Rate limit periodic intervals") already, but that fix got
lost in a later rework.
Reported-by: syzbot+b9564ba6e8e00694511b@syzkaller.appspotmail.com
Fixes: f2c45807d3 ("alarmtimer: Switch over to generic set/get/rearm routine")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87k00q1no2.ffs@tglx
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
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 <ubizjak@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230116165337.5810-1-ubizjak@gmail.com
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 <dave@stgolabs.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230123173206.6764-3-dave@stgolabs.net
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 <feng.tang@intel.com>
Acked-by: Waiman Long <longman@redhat.com>
Cc: John Stultz <jstultz@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Feng Tang <feng.tang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
