| Age | Commit message (Collapse) | Author |
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fixes from Ingo Molnar:
"Fix a PREEMPT_RT bug in the clocksource verification code that caused
false positive warnings.
Also fix a timer migration setup bug when new CPUs are added"
* tag 'timers-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timers/migration: Fix off-by-one root mis-connection
clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context
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Before attaching a new root to the old root, the children counter of the
new root is checked to verify that only the upcoming CPU's top group have
been connected to it. However since the recently added commit b729cc1ec21a
("timers/migration: Fix another race between hotplug and idle entry/exit")
this check is not valid anymore because the old root is pre-accounted
as a child to the new root. Therefore after connecting the upcoming
CPU's top group to the new root, the children count to be expected must
be 2 and not 1 anymore.
This omission results in the old root to not be connected to the new
root. Then eventually the system may run with more than one top level,
which defeats the purpose of a single idle migrator.
Also the old root is pre-accounted but not connected upon the new root
creation. But it can be connected to the new root later on. Therefore
the old root may be accounted twice to the new root. The propagation of
such overcommit can end up creating a double final top-level root with a
groupmask incorrectly initialized. Although harmless given that the final
top level roots will never have a parent to walk up to, this oddity
opportunistically reported the core issue:
WARNING: CPU: 8 PID: 0 at kernel/time/timer_migration.c:543 tmigr_requires_handle_remote
CPU: 8 UID: 0 PID: 0 Comm: swapper/8
RIP: 0010:tmigr_requires_handle_remote
Call Trace:
<IRQ>
? tmigr_requires_handle_remote
? hrtimer_run_queues
update_process_times
tick_periodic
tick_handle_periodic
__sysvec_apic_timer_interrupt
sysvec_apic_timer_interrupt
</IRQ>
Fix the problem by taking the old root into account in the children count
of the new root so the connection is not omitted.
Also warn when more than one top level group exists to better detect
similar issues in the future.
Fixes: b729cc1ec21a ("timers/migration: Fix another race between hotplug and idle entry/exit")
Reported-by: Matt Fleming <mfleming@cloudflare.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250205160220.39467-1-frederic@kernel.org
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fixes from Thomas Gleixner:
- Properly cast the input to secs_to_jiffies() to unsigned long as
otherwise the result uses the data type of the input variable, which
causes result range checks to fail if the input data type is signed
and smaller than unsigned long.
- Handle late armed hrtimers gracefully on CPU hotplug
There are legitimate cases where a hrtimer is (re)armed on an
outgoing CPU after the timers have been migrated away. This triggers
warnings and caused people to implement horrible workarounds in RCU.
But those workarounds are incomplete and do not cover e.g. the
scheduler hrtimers.
Stop this by force moving timer which are enqueued on the current CPU
after timer migration to be queued on a remote online CPU.
This allows to undo the workarounds in a seperate step.
- Demote a warning level printk() to info level in the clocksource
watchdog code as there is no point to emit a warning level message
for a purely informational message.
- Mark a helper function __always_inline and move it into the existing
#ifdef block to avoid 'unused function' warnings from CLANG
* tag 'timers-urgent-2025-02-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
jiffies: Cast to unsigned long in secs_to_jiffies() conversion
clocksource: Use pr_info() for "Checking clocksource synchronization" message
hrtimers: Force migrate away hrtimers queued after CPUHP_AP_HRTIMERS_DYING
hrtimers: Mark is_migration_base() with __always_inline
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atomic context
The following bug report happened with a PREEMPT_RT kernel:
BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2012, name: kwatchdog
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
get_random_u32+0x4f/0x110
clocksource_verify_choose_cpus+0xab/0x1a0
clocksource_verify_percpu.part.0+0x6b/0x330
clocksource_watchdog_kthread+0x193/0x1a0
It is due to the fact that clocksource_verify_choose_cpus() is invoked with
preemption disabled. This function invokes get_random_u32() to obtain
random numbers for choosing CPUs. The batched_entropy_32 local lock and/or
the base_crng.lock spinlock in driver/char/random.c will be acquired during
the call. In PREEMPT_RT kernel, they are both sleeping locks and so cannot
be acquired in atomic context.
Fix this problem by using migrate_disable() to allow smp_processor_id() to
be reliably used without introducing atomic context. preempt_disable() is
then called after clocksource_verify_choose_cpus() but before the
clocksource measurement is being run to avoid introducing unexpected
latency.
Fixes: 7560c02bdffb ("clocksource: Check per-CPU clock synchronization when marked unstable")
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/all/20250131173323.891943-2-longman@redhat.com
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Add the const qualifier to all the ctl_tables in the tree except for
watchdog_hardlockup_sysctl, memory_allocation_profiling_sysctls,
loadpin_sysctl_table and the ones calling register_net_sysctl (./net,
drivers/inifiniband dirs). These are special cases as they use a
registration function with a non-const qualified ctl_table argument or
modify the arrays before passing them on to the registration function.
Constifying ctl_table structs will prevent the modification of
proc_handler function pointers as the arrays would reside in .rodata.
This is made possible after commit 78eb4ea25cd5 ("sysctl: treewide:
constify the ctl_table argument of proc_handlers") constified all the
proc_handlers.
Created this by running an spatch followed by a sed command:
Spatch:
virtual patch
@
depends on !(file in "net")
disable optional_qualifier
@
identifier table_name != {
watchdog_hardlockup_sysctl,
iwcm_ctl_table,
ucma_ctl_table,
memory_allocation_profiling_sysctls,
loadpin_sysctl_table
};
@@
+ const
struct ctl_table table_name [] = { ... };
sed:
sed --in-place \
-e "s/struct ctl_table .table = &uts_kern/const struct ctl_table *table = \&uts_kern/" \
kernel/utsname_sysctl.c
Reviewed-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> # for kernel/trace/
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> # SCSI
Reviewed-by: Darrick J. Wong <djwong@kernel.org> # xfs
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>
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The "Checking clocksource synchronization" message is normally printed
when clocksource_verify_percpu() is called for a given clocksource if
both the CLOCK_SOURCE_UNSTABLE and CLOCK_SOURCE_VERIFY_PERCPU flags
are set.
It is an informational message and so pr_info() is the correct choice.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250125015442.3740588-1-longman@redhat.com
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hrtimers are migrated away from the dying CPU to any online target at
the CPUHP_AP_HRTIMERS_DYING stage in order not to delay bandwidth timers
handling tasks involved in the CPU hotplug forward progress.
However wakeups can still be performed by the outgoing CPU after
CPUHP_AP_HRTIMERS_DYING. Those can result again in bandwidth timers being
armed. Depending on several considerations (crystal ball power management
based election, earliest timer already enqueued, timer migration enabled or
not), the target may eventually be the current CPU even if offline. If that
happens, the timer is eventually ignored.
The most notable example is RCU which had to deal with each and every of
those wake-ups by deferring them to an online CPU, along with related
workarounds:
_ e787644caf76 (rcu: Defer RCU kthreads wakeup when CPU is dying)
_ 9139f93209d1 (rcu/nocb: Fix RT throttling hrtimer armed from offline CPU)
_ f7345ccc62a4 (rcu/nocb: Fix rcuog wake-up from offline softirq)
The problem isn't confined to RCU though as the stop machine kthread
(which runs CPUHP_AP_HRTIMERS_DYING) reports its completion at the end
of its work through cpu_stop_signal_done() and performs a wake up that
eventually arms the deadline server timer:
WARNING: CPU: 94 PID: 588 at kernel/time/hrtimer.c:1086 hrtimer_start_range_ns+0x289/0x2d0
CPU: 94 UID: 0 PID: 588 Comm: migration/94 Not tainted
Stopper: multi_cpu_stop+0x0/0x120 <- stop_machine_cpuslocked+0x66/0xc0
RIP: 0010:hrtimer_start_range_ns+0x289/0x2d0
Call Trace:
<TASK>
start_dl_timer
enqueue_dl_entity
dl_server_start
enqueue_task_fair
enqueue_task
ttwu_do_activate
try_to_wake_up
complete
cpu_stopper_thread
Instead of providing yet another bandaid to work around the situation, fix
it in the hrtimers infrastructure instead: always migrate away a timer to
an online target whenever it is enqueued from an offline CPU.
This will also allow to revert all the above RCU disgraceful hacks.
Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Reported-by: Vlad Poenaru <vlad.wing@gmail.com>
Reported-by: Usama Arif <usamaarif642@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/all/20250117232433.24027-1-frederic@kernel.org
Closes: 20241213203739.1519801-1-usamaarif642@gmail.com
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When is_migration_base() is unused, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y:
kernel/time/hrtimer.c:156:20: error: unused function 'is_migration_base' [-Werror,-Wunused-function]
156 | static inline bool is_migration_base(struct hrtimer_clock_base *base)
| ^~~~~~~~~~~~~~~~~
Fix this by marking it with __always_inline.
[ tglx: Use __always_inline instead of __maybe_unused and move it into the
usage sites conditional ]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250116160745.243358-1-andriy.shevchenko@linux.intel.com
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer and timekeeping updates from Thomas Gleixner:
- Just boring cleanups, typo and comment fixes and trivial optimizations
* tag 'timers-core-2025-01-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timers/migration: Simplify top level detection on group setup
timers: Optimize get_timer_[this_]cpu_base()
timekeeping: Remove unused ktime_get_fast_timestamps()
timer/migration: Fix kernel-doc warnings for union tmigr_state
tick/broadcast: Add kernel-doc for function parameters
hrtimers: Update the return type of enqueue_hrtimer()
clocksource/wdtest: Print time values for short udelay(1)
posix-timers: Fix typo in __lock_timer()
vdso: Correct typo in PAGE_SHIFT comment
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Having a single group on a given level is enough to know this is the
top level, because a root has to have at least two children, unless that
root is the only group and the children are actual CPUs.
Simplify the test in tmigr_setup_groups() accordingly.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250114231507.21672-5-frederic@kernel.org
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Consider a scenario where a CPU transitions from CPUHP_ONLINE to halfway
through a CPU hotunplug down to CPUHP_HRTIMERS_PREPARE, and then back to
CPUHP_ONLINE:
Since hrtimers_prepare_cpu() does not run, cpu_base.hres_active remains set
to 1 throughout. However, during a CPU unplug operation, the tick and the
clockevents are shut down at CPUHP_AP_TICK_DYING. On return to the online
state, for instance CFS incorrectly assumes that the hrtick is already
active, and the chance of the clockevent device to transition to oneshot
mode is also lost forever for the CPU, unless it goes back to a lower state
than CPUHP_HRTIMERS_PREPARE once.
This round-trip reveals another issue; cpu_base.online is not set to 1
after the transition, which appears as a WARN_ON_ONCE in enqueue_hrtimer().
Aside of that, the bulk of the per CPU state is not reset either, which
means there are dangling pointers in the worst case.
Address this by adding a corresponding startup() callback, which resets the
stale per CPU state and sets the online flag.
[ tglx: Make the new callback unconditionally available, remove the online
modification in the prepare() callback and clear the remaining
state in the starting callback instead of the prepare callback ]
Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20241220134421.3809834-1-koichiro.den@canonical.com
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The group's ignore flag is:
_ read under the group's lock (idle entry, remote expiry)
_ turned on/off under the group's lock (idle entry, remote expiry)
_ turned on locklessly on idle exit
When idle entry or remote expiry clear the "ignore" flag of a group, the
operation must be synchronized against other concurrent idle entry or
remote expiry to make sure the related group timer is never missed. To
enforce this synchronization, both "ignore" clear and read are
performed under the group lock.
On the contrary, whether idle entry or remote expiry manage to observe
the "ignore" flag turned on by a CPU exiting idle is a matter of
optimization. If that flag set is missed or cleared concurrently, the
worst outcome is a migrator wasting time remotely handling a "ghost"
timer. This is why the ignore flag can be set locklessly.
Unfortunately, the related lockless accesses are bare and miss
appropriate annotations. KCSAN rightfully complains:
BUG: KCSAN: data-race in __tmigr_cpu_activate / print_report
write to 0xffff88842fc28004 of 1 bytes by task 0 on cpu 0:
__tmigr_cpu_activate
tmigr_cpu_activate
timer_clear_idle
tick_nohz_restart_sched_tick
tick_nohz_idle_exit
do_idle
cpu_startup_entry
kernel_init
do_initcalls
clear_bss
reserve_bios_regions
common_startup_64
read to 0xffff88842fc28004 of 1 bytes by task 0 on cpu 1:
print_report
kcsan_report_known_origin
kcsan_setup_watchpoint
tmigr_next_groupevt
tmigr_update_events
tmigr_inactive_up
__walk_groups+0x50/0x77
walk_groups
__tmigr_cpu_deactivate
tmigr_cpu_deactivate
__get_next_timer_interrupt
timer_base_try_to_set_idle
tick_nohz_stop_tick
tick_nohz_idle_stop_tick
cpuidle_idle_call
do_idle
Although the relevant accesses could be marked as data_race(), the
"ignore" flag being read several times within the same
tmigr_update_events() function is confusing and error prone. Prefer
reading it once in that function and make use of similar/paired accesses
elsewhere with appropriate comments when necessary.
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250114231507.21672-4-frederic@kernel.org
Closes: https://lore.kernel.org/oe-lkp/202501031612.62e0c498-lkp@intel.com
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Commit 2522c84db513 ("timers/migration: Fix another race between hotplug
and idle entry/exit") fixed yet another race between idle exit and CPU
hotplug up leading to a wrong "0" value migrator assigned to the top
level. However there is yet another situation that remains unhandled:
[GRP0:0]
migrator = TMIGR_NONE
active = NONE
groupmask = 1
/ \ \
0 1 2..7
idle idle idle
0) The system is fully idle.
[GRP0:0]
migrator = CPU 0
active = CPU 0
groupmask = 1
/ \ \
0 1 2..7
active idle idle
1) CPU 0 is activating. It has done the cmpxchg on the top's ->migr_state
but it hasn't yet returned to __walk_groups().
[GRP0:0]
migrator = CPU 0
active = CPU 0, CPU 1
groupmask = 1
/ \ \
0 1 2..7
active active idle
2) CPU 1 is activating. CPU 0 stays the migrator (still stuck in
__walk_groups(), delayed by #VMEXIT for example).
[GRP1:0]
migrator = TMIGR_NONE
active = NONE
groupmask = 1
/ \
[GRP0:0] [GRP0:1]
migrator = CPU 0 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = NONE
groupmask = 1 groupmask = 2
/ \ \
0 1 2..7 8
active active idle !online
3) CPU 8 is preparing to boot. CPUHP_TMIGR_PREPARE is being ran by CPU 1
which has created the GRP0:1 and the new top GRP1:0 connected to GRP0:1
and GRP0:0. CPU 1 hasn't yet propagated its activation up to GRP1:0.
[GRP1:0]
migrator = GRP0:0
active = GRP0:0
groupmask = 1
/ \
[GRP0:0] [GRP0:1]
migrator = CPU 0 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = NONE
groupmask = 1 groupmask = 2
/ \ \
0 1 2..7 8
active active idle !online
4) CPU 0 finally resumed after its #VMEXIT. It's in __walk_groups()
returning from tmigr_cpu_active(). The new top GRP1:0 is visible and
fetched and the pre-initialized groupmask of GRP0:0 is also visible.
As a result tmigr_active_up() is called to GRP1:0 with GRP0:0 as active
and migrator. CPU 0 is returning to __walk_groups() but suffers again
a #VMEXIT.
[GRP1:0]
migrator = GRP0:0
active = GRP0:0
groupmask = 1
/ \
[GRP0:0] [GRP0:1]
migrator = CPU 0 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = NONE
groupmask = 1 groupmask = 2
/ \ \
0 1 2..7 8
active active idle !online
5) CPU 1 propagates its activation of GRP0:0 to GRP1:0. This has no
effect since CPU 0 did it already.
[GRP1:0]
migrator = GRP0:0
active = GRP0:0, GRP0:1
groupmask = 1
/ \
[GRP0:0] [GRP0:1]
migrator = CPU 0 migrator = CPU 8
active = CPU 0, CPU1 active = CPU 8
groupmask = 1 groupmask = 2
/ \ \ \
0 1 2..7 8
active active idle active
6) CPU 1 links CPU 8 to its group. CPU 8 boots and goes through
CPUHP_AP_TMIGR_ONLINE which propagates activation.
[GRP2:0]
migrator = TMIGR_NONE
active = NONE
groupmask = 1
/ \
[GRP1:0] [GRP1:1]
migrator = GRP0:0 migrator = TMIGR_NONE
active = GRP0:0, GRP0:1 active = NONE
groupmask = 1 groupmask = 2
/ \
[GRP0:0] [GRP0:1] [GRP0:2]
migrator = CPU 0 migrator = CPU 8 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = CPU 8 active = NONE
groupmask = 1 groupmask = 2 groupmask = 0
/ \ \ \
0 1 2..7 8 64
active active idle active !online
7) CPU 64 is booting. CPUHP_TMIGR_PREPARE is being ran by CPU 1
which has created the GRP1:1, GRP0:2 and the new top GRP2:0 connected to
GRP1:1 and GRP1:0. CPU 1 hasn't yet propagated its activation up to
GRP2:0.
[GRP2:0]
migrator = 0 (!!!)
active = NONE
groupmask = 1
/ \
[GRP1:0] [GRP1:1]
migrator = GRP0:0 migrator = TMIGR_NONE
active = GRP0:0, GRP0:1 active = NONE
groupmask = 1 groupmask = 2
/ \
[GRP0:0] [GRP0:1] [GRP0:2]
migrator = CPU 0 migrator = CPU 8 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = CPU 8 active = NONE
groupmask = 1 groupmask = 2 groupmask = 0
/ \ \ \
0 1 2..7 8 64
active active idle active !online
8) CPU 0 finally resumed after its #VMEXIT. It's in __walk_groups()
returning from tmigr_cpu_active(). The new top GRP2:0 is visible and
fetched but the pre-initialized groupmask of GRP1:0 is not because no
ordering made its initialization visible. As a result tmigr_active_up()
may be called to GRP2:0 with a "0" child's groumask. Leaving the timers
ignored for ever when the system is fully idle.
The race is highly theoretical and perhaps impossible in practice but
the groupmask of the child is not the only concern here as the whole
initialization of the child is not guaranteed to be visible to any
tree walker racing against hotplug (idle entry/exit, remote handling,
etc...). Although the current code layout seem to be resilient to such
hazards, this doesn't tell much about the future.
Fix this with enforcing address dependency between group initialization
and the write/read to the group's parent's pointer. Fortunately that
doesn't involve any barrier addition in the fast paths.
Fixes: 10a0e6f3d3db ("timers/migration: Move hierarchy setup into cpuhotplug prepare callback")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250114231507.21672-3-frederic@kernel.org
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Commit 10a0e6f3d3db ("timers/migration: Move hierarchy setup into
cpuhotplug prepare callback") fixed a race between idle exit and CPU
hotplug up leading to a wrong "0" value migrator assigned to the top
level. However there is still a situation that remains unhandled:
[GRP0:0]
migrator = TMIGR_NONE
active = NONE
groupmask = 0
/ \ \
0 1 2..7
idle idle idle
0) The system is fully idle.
[GRP0:0]
migrator = CPU 0
active = CPU 0
groupmask = 0
/ \ \
0 1 2..7
active idle idle
1) CPU 0 is activating. It has done the cmpxchg on the top's ->migr_state
but it hasn't yet returned to __walk_groups().
[GRP0:0]
migrator = CPU 0
active = CPU 0, CPU 1
groupmask = 0
/ \ \
0 1 2..7
active active idle
2) CPU 1 is activating. CPU 0 stays the migrator (still stuck in
__walk_groups(), delayed by #VMEXIT for example).
[GRP1:0]
migrator = TMIGR_NONE
active = NONE
groupmask = 0
/ \
[GRP0:0] [GRP0:1]
migrator = CPU 0 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = NONE
groupmask = 2 groupmask = 1
/ \ \
0 1 2..7 8
active active idle !online
3) CPU 8 is preparing to boot. CPUHP_TMIGR_PREPARE is being ran by CPU 1
which has created the GRP0:1 and the new top GRP1:0 connected to GRP0:1
and GRP0:0. The groupmask of GRP0:0 is now 2. CPU 1 hasn't yet
propagated its activation up to GRP1:0.
[GRP1:0]
migrator = 0 (!!!)
active = NONE
groupmask = 0
/ \
[GRP0:0] [GRP0:1]
migrator = CPU 0 migrator = TMIGR_NONE
active = CPU 0, CPU1 active = NONE
groupmask = 2 groupmask = 1
/ \ \
0 1 2..7 8
active active idle !online
4) CPU 0 finally resumed after its #VMEXIT. It's in __walk_groups()
returning from tmigr_cpu_active(). The new top GRP1:0 is visible and
fetched but the freshly updated groupmask of GRP0:0 may not be visible
due to lack of ordering! As a result tmigr_active_up() is called to
GRP0:0 with a child's groupmask of "0". This buggy "0" groupmask then
becomes the migrator for GRP1:0 forever. As a result, timers on a fully
idle system get ignored.
One possible fix would be to define TMIGR_NONE as "0" so that such a
race would have no effect. And after all TMIGR_NONE doesn't need to be
anything else. However this would leave an uncomfortable state machine
where gears happen not to break by chance but are vulnerable to future
modifications.
Keep TMIGR_NONE as is instead and pre-initialize to "1" the groupmask of
any newly created top level. This groupmask is guaranteed to be visible
upon fetching the corresponding group for the 1st time:
_ By the upcoming CPU thanks to CPU hotplug synchronization between the
control CPU (BP) and the booting one (AP).
_ By the control CPU since the groupmask and parent pointers are
initialized locally.
_ By all CPUs belonging to the same group than the control CPU because
they must wait for it to ever become idle before needing to walk to
the new top. The cmpcxhg() on ->migr_state then makes sure its
groupmask is visible.
With this pre-initialization, it is guaranteed that if a future top level
is linked to an old one, it is walked through with a valid groupmask.
Fixes: 10a0e6f3d3db ("timers/migration: Move hierarchy setup into cpuhotplug prepare callback")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250114231507.21672-2-frederic@kernel.org
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If a timer is deferrable and NO_HZ_COMMON is enabled, get_timer_cpu_base()
and get_timer_this_cpu_base() invoke per_cpu_ptr() and this_cpu_ptr()
twice.
While this seems to be cheap, get_timer_cpu_base() can be called in a loop
in lock_timer_base().
Optimize the functions by updating the base index for deferrable timers and
retrieving the actual base pointer once.
In both cases the resulting assembly code of those helpers becomes smaller,
which results in a ~30% execution time reduction for a lock_timer_base()
micro bench mark.
Signed-off-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241231150115.1978342-1-quic_zhonhan@quicinc.com
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ktime_get_fast_timestamps() was added in 2020 by commit e2d977c9f1ab
("timekeeping: Provide multi-timestamp accessor to NMI safe timekeeper")
but has remained unused.
Remove it.
[ tglx: Fold the inline as David suggested in the submission ]
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250112160132.450209-1-linux@treblig.org
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Use the correct kernel-doc notation for nested structs/unions to
eliminate warnings:
timer_migration.h:119: warning: Incorrect use of kernel-doc format: * struct - split state of tmigr_group
timer_migration.h:134: warning: Function parameter or struct member 'active' not described in 'tmigr_state'
timer_migration.h:134: warning: Function parameter or struct member 'migrator' not described in 'tmigr_state'
timer_migration.h:134: warning: Function parameter or struct member 'seq' not described in 'tmigr_state'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250111063156.910903-1-rdunlap@infradead.org
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Add kernel-doc comments for two parameters to eliminate kernel-doc warnings:
tick-broadcast.c:1026: warning: Function parameter or struct member 'bc' not described in 'tick_broadcast_setup_oneshot'
tick-broadcast.c:1026: warning: Function parameter or struct member 'from_periodic' not described in 'tick_broadcast_setup_oneshot'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250111063148.910887-1-rdunlap@infradead.org
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|
The return type should be 'bool' instead of 'int' according to the calling
context in the kernel, and its internal implementation, i.e. :
return timerqueue_add();
which is a bool-return function.
[ tglx: Adjust function arguments ]
Signed-off-by: Richard Clark <richard.xnu.clark@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/Z2ppT7me13dtxm1a@MBC02GN1V4Q05P
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When a pair of clocksource reads separated by a udelay(1) claim less than a
full microsecond of elapsed time, print the measured delay as part of the
splat.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/717a2ddf-a80f-490b-aa3a-4e4b74fa56ca@paulmck-laptop
|
|
The word 'accross' is wrong, so fix it.
Signed-off-by: Zhu Jun <zhujun2@cmss.chinamobile.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241204080907.11989-1-zhujun2@cmss.chinamobile.com
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Guenter reported boot stalls on a emulated ARM 32-bit platform, which has a
24-bit wide clocksource.
It turns out that the calculated maximal idle time, which limits idle
sleeps to prevent clocksource wrap arounds, is close to the point where the
negative motion detection triggers.
max_idle_ns: 597268854 ns
negative motion tripping point: 671088640 ns
If the idle wakeup is delayed beyond that point, the clocksource
advances far enough to trigger the negative motion detection. This
prevents the clock to advance and in the worst case the system stalls
completely if the consecutive sleeps based on the stale clock are
delayed as well.
Cure this by calculating a more robust cut-off value for negative motion,
which covers 87.5% of the actual clocksource counter width. Compare the
delta against this value to catch negative motion. This is specifically for
clock sources with a small counter width as their wrap around time is close
to the half counter width. For clock sources with wide counters this is not
a problem because the maximum idle time is far from the half counter width
due to the math overflow protection constraints.
For the case at hand this results in a tripping point of 1174405120ns.
Note, that this cannot prevent issues when the delay exceeds the 87.5%
margin, but that's not different from the previous unchecked version which
allowed arbitrary time jumps.
Systems with small counter width are prone to invalid results, but this
problem is unlikely to be seen on real hardware. If such a system
completely stalls for more than half a second, then there are other more
urgent problems than the counter wrapping around.
Fixes: c163e40af9b2 ("timekeeping: Always check for negative motion")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/all/8734j5ul4x.ffs@tglx
Closes: https://lore.kernel.org/all/387b120b-d68a-45e8-b6ab-768cd95d11c2@roeck-us.net
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Due to an unsigned cast, adjtimex() returns the wrong offest when using
ADJ_MICRO and the offset is negative. In this case a small negative offset
returns approximately 4.29 seconds (~ 2^32/1000 milliseconds) due to the
unsigned cast of the negative offset.
This cast was added when the kernel internal struct timex was changed to
use type long long for the time offset value to address the problem of a
64bit/32bit division on 32bit systems.
The correct cast would have been (s32), which is correct as time_offset can
only be in the range of [INT_MIN..INT_MAX] because the shift constant used
for calculating it is 32. But that's non-obvious.
Remove the cast and use div_s64() to cure the issue.
[ tglx: Fix white space damage, use div_s64() and amend the change log ]
Fixes: ead25417f82e ("timex: use __kernel_timex internally")
Signed-off-by: Marcelo Dalmas <marcelo.dalmas@ge.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/SJ0P101MB03687BF7D5A10FD3C49C51E5F42E2@SJ0P101MB0368.NAMP101.PROD.OUTLOOK.COM
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer updates from Thomas Gleixner:
"A rather large update for timekeeping and timers:
- The final step to get rid of auto-rearming posix-timers
posix-timers are currently auto-rearmed by the kernel when the
signal of the timer is ignored so that the timer signal can be
delivered once the corresponding signal is unignored.
This requires to throttle the timer to prevent a DoS by small
intervals and keeps the system pointlessly out of low power states
for no value. This is a long standing non-trivial problem due to
the lock order of posix-timer lock and the sighand lock along with
life time issues as the timer and the sigqueue have different life
time rules.
Cure this by:
- Embedding the sigqueue into the timer struct to have the same
life time rules. Aside of that this also avoids the lookup of
the timer in the signal delivery and rearm path as it's just a
always valid container_of() now.
- Queuing ignored timer signals onto a seperate ignored list.
- Moving queued timer signals onto the ignored list when the
signal is switched to SIG_IGN before it could be delivered.
- Walking the ignored list when SIG_IGN is lifted and requeue the
signals to the actual signal lists. This allows the signal
delivery code to rearm the timer.
This also required to consolidate the signal delivery rules so they
are consistent across all situations. With that all self test
scenarios finally succeed.
- Core infrastructure for VFS multigrain timestamping
This is required to allow the kernel to use coarse grained time
stamps by default and switch to fine grained time stamps when inode
attributes are actively observed via getattr().
These changes have been provided to the VFS tree as well, so that
the VFS specific infrastructure could be built on top.
- Cleanup and consolidation of the sleep() infrastructure
- Move all sleep and timeout functions into one file
- Rework udelay() and ndelay() into proper documented inline
functions and replace the hardcoded magic numbers by proper
defines.
- Rework the fsleep() implementation to take the reality of the
timer wheel granularity on different HZ values into account.
Right now the boundaries are hard coded time ranges which fail
to provide the requested accuracy on different HZ settings.
- Update documentation for all sleep/timeout related functions
and fix up stale documentation links all over the place
- Fixup a few usage sites
- Rework of timekeeping and adjtimex(2) to prepare for multiple PTP
clocks
A system can have multiple PTP clocks which are participating in
seperate and independent PTP clock domains. So far the kernel only
considers the PTP clock which is based on CLOCK TAI relevant as
that's the clock which drives the timekeeping adjustments via the
various user space daemons through adjtimex(2).
The non TAI based clock domains are accessible via the file
descriptor based posix clocks, but their usability is very limited.
They can't be accessed fast as they always go all the way out to
the hardware and they cannot be utilized in the kernel itself.
As Time Sensitive Networking (TSN) gains traction it is required to
provide fast user and kernel space access to these clocks.
The approach taken is to utilize the timekeeping and adjtimex(2)
infrastructure to provide this access in a similar way how the
kernel provides access to clock MONOTONIC, REALTIME etc.
Instead of creating a duplicated infrastructure this rework
converts timekeeping and adjtimex(2) into generic functionality
which operates on pointers to data structures instead of using
static variables.
This allows to provide time accessors and adjtimex(2) functionality
for the independent PTP clocks in a subsequent step.
- Consolidate hrtimer initialization
hrtimers are set up by initializing the data structure and then
seperately setting the callback function for historical reasons.
That's an extra unnecessary step and makes Rust support less
straight forward than it should be.
Provide a new set of hrtimer_setup*() functions and convert the
core code and a few usage sites of the less frequently used
interfaces over.
The bulk of the htimer_init() to hrtimer_setup() conversion is
already prepared and scheduled for the next merge window.
- Drivers:
- Ensure that the global timekeeping clocksource is utilizing the
cluster 0 timer on MIPS multi-cluster systems.
Otherwise CPUs on different clusters use their cluster specific
clocksource which is not guaranteed to be synchronized with
other clusters.
- Mostly boring cleanups, fixes, improvements and code movement"
* tag 'timers-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (140 commits)
posix-timers: Fix spurious warning on double enqueue versus do_exit()
clocksource/drivers/arm_arch_timer: Use of_property_present() for non-boolean properties
clocksource/drivers/gpx: Remove redundant casts
clocksource/drivers/timer-ti-dm: Fix child node refcount handling
dt-bindings: timer: actions,owl-timer: convert to YAML
clocksource/drivers/ralink: Add Ralink System Tick Counter driver
clocksource/drivers/mips-gic-timer: Always use cluster 0 counter as clocksource
clocksource/drivers/timer-ti-dm: Don't fail probe if int not found
clocksource/drivers:sp804: Make user selectable
clocksource/drivers/dw_apb: Remove unused dw_apb_clockevent functions
hrtimers: Delete hrtimer_init_on_stack()
alarmtimer: Switch to use hrtimer_setup() and hrtimer_setup_on_stack()
io_uring: Switch to use hrtimer_setup_on_stack()
sched/idle: Switch to use hrtimer_setup_on_stack()
hrtimers: Delete hrtimer_init_sleeper_on_stack()
wait: Switch to use hrtimer_setup_sleeper_on_stack()
timers: Switch to use hrtimer_setup_sleeper_on_stack()
net: pktgen: Switch to use hrtimer_setup_sleeper_on_stack()
futex: Switch to use hrtimer_setup_sleeper_on_stack()
fs/aio: Switch to use hrtimer_setup_sleeper_on_stack()
...
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull vdso data page handling updates from Thomas Gleixner:
"First steps of consolidating the VDSO data page handling.
The VDSO data page handling is architecture specific for historical
reasons, but there is no real technical reason to do so.
Aside of that VDSO data has become a dump ground for various
mechanisms and fail to provide a clear separation of the
functionalities.
Clean this up by:
- consolidating the VDSO page data by getting rid of architecture
specific warts especially in x86 and PowerPC.
- removing the last includes of header files which are pulling in
other headers outside of the VDSO namespace.
- seperating timekeeping and other VDSO data accordingly.
Further consolidation of the VDSO page handling is done in subsequent
changes scheduled for the next merge window.
This also lays the ground for expanding the VDSO time getters for
independent PTP clocks in a generic way without making every
architecture add support seperately"
* tag 'timers-vdso-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (42 commits)
x86/vdso: Add missing brackets in switch case
vdso: Rename struct arch_vdso_data to arch_vdso_time_data
powerpc: Split systemcfg struct definitions out from vdso
powerpc: Split systemcfg data out of vdso data page
powerpc: Add kconfig option for the systemcfg page
powerpc/pseries/lparcfg: Use num_possible_cpus() for potential processors
powerpc/pseries/lparcfg: Fix printing of system_active_processors
powerpc/procfs: Propagate error of remap_pfn_range()
powerpc/vdso: Remove offset comment from 32bit vdso_arch_data
x86/vdso: Split virtual clock pages into dedicated mapping
x86/vdso: Delete vvar.h
x86/vdso: Access vdso data without vvar.h
x86/vdso: Move the rng offset to vsyscall.h
x86/vdso: Access rng vdso data without vvar.h
x86/vdso: Access timens vdso data without vvar.h
x86/vdso: Allocate vvar page from C code
x86/vdso: Access rng data from kernel without vvar
x86/vdso: Place vdso_data at beginning of vvar page
x86/vdso: Use __arch_get_vdso_data() to access vdso data
x86/mm/mmap: Remove arch_vma_name()
...
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull interrupt subsystem updates from Thomas Gleixner:
"Tree wide:
- Make nr_irqs static to the core code and provide accessor functions
to remove existing and prevent future aliasing problems with local
variables or function arguments of the same name.
Core code:
- Prevent freeing an interrupt in the devres code which is not
managed by devres in the first place.
- Use seq_put_decimal_ull_width() for decimal values output in
/proc/interrupts which increases performance significantly as it
avoids parsing the format strings over and over.
- Optimize raising the timer and hrtimer soft interrupts by using the
'set bit only' variants instead of the combined version which
checks whether ksoftirqd should be woken up. The latter is a
pointless exercise as both soft interrupts are raised in the
context of the timer interrupt and therefore never wake up
ksoftirqd.
- Delegate timer/hrtimer soft interrupt processing to a dedicated
thread on RT.
Timer and hrtimer soft interrupts are always processed in ksoftirqd
on RT enabled kernels. This can lead to high latencies when other
soft interrupts are delegated to ksoftirqd as well.
The separate thread allows to run them seperately under a RT
scheduling policy to reduce the latency overhead.
Drivers:
- New drivers or extensions of existing drivers to support Renesas
RZ/V2H(P), Aspeed AST27XX, T-HEAD C900 and ATMEL sam9x7 interrupt
chips
- Support for multi-cluster GICs on MIPS.
MIPS CPUs can come with multiple CPU clusters, where each CPU
cluster has its own GIC (Generic Interrupt Controller). This
requires to access the GIC of a remote cluster through a redirect
register block.
This is encapsulated into a set of helper functions to keep the
complexity out of the actual code paths which handle the GIC
details.
- Support for encrypted guests in the ARM GICV3 ITS driver
The ITS page needs to be shared with the hypervisor and therefore
must be decrypted.
- Small cleanups and fixes all over the place"
* tag 'irq-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (50 commits)
irqchip/riscv-aplic: Prevent crash when MSI domain is missing
genirq/proc: Use seq_put_decimal_ull_width() for decimal values
softirq: Use a dedicated thread for timer wakeups on PREEMPT_RT.
timers: Use __raise_softirq_irqoff() to raise the softirq.
hrtimer: Use __raise_softirq_irqoff() to raise the softirq
riscv: defconfig: Enable T-HEAD C900 ACLINT SSWI drivers
irqchip: Add T-HEAD C900 ACLINT SSWI driver
dt-bindings: interrupt-controller: Add T-HEAD C900 ACLINT SSWI device
irqchip/stm32mp-exti: Use of_property_present() for non-boolean properties
irqchip/mips-gic: Fix selection of GENERIC_IRQ_EFFECTIVE_AFF_MASK
irqchip/mips-gic: Prevent indirect access to clusters without CPU cores
irqchip/mips-gic: Multi-cluster support
irqchip/mips-gic: Setup defaults in each cluster
irqchip/mips-gic: Support multi-cluster in for_each_online_cpu_gic()
irqchip/mips-gic: Replace open coded online CPU iterations
genirq/irqdesc: Use str_enabled_disabled() helper in wakeup_show()
genirq/devres: Don't free interrupt which is not managed by devres
irqchip/gic-v3-its: Fix over allocation in itt_alloc_pool()
irqchip/aspeed-intc: Add AST27XX INTC support
dt-bindings: interrupt-controller: Add support for ASPEED AST27XX INTC
...
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
"Lockdep:
- Enable PROVE_RAW_LOCK_NESTING with PROVE_LOCKING (Sebastian Andrzej
Siewior)
- Add lockdep_cleanup_dead_cpu() (David Woodhouse)
futexes:
- Use atomic64_inc_return() in get_inode_sequence_number() (Uros
Bizjak)
- Use atomic64_try_cmpxchg_relaxed() in get_inode_sequence_number()
(Uros Bizjak)
RT locking:
- Add sparse annotation PREEMPT_RT's locking (Sebastian Andrzej
Siewior)
spinlocks:
- Use atomic_try_cmpxchg_release() in osq_unlock() (Uros Bizjak)
atomics:
- x86: Use ALT_OUTPUT_SP() for __alternative_atomic64() (Uros Bizjak)
- x86: Use ALT_OUTPUT_SP() for __arch_{,try_}cmpxchg64_emu() (Uros
Bizjak)
KCSAN, seqlocks:
- Support seqcount_latch_t (Marco Elver)
<linux/cleanup.h>:
- Add if_not_guard() conditional guard helper (David Lechner)
- Adjust scoped_guard() macros to avoid potential warning (Przemek
Kitszel)
- Remove address space of returned pointer (Uros Bizjak)
WW mutexes:
- locking/ww_mutex: Adjust to lockdep nest_lock requirements (Thomas
Hellström)
Rust integration:
- Fix raw_spin_lock initialization on PREEMPT_RT (Eder Zulian)
Misc cleanups & fixes:
- lockdep: Fix wait-type check related warnings (Ahmed Ehab)
- lockdep: Use info level for initial info messages (Jiri Slaby)
- spinlocks: Make __raw_* lock ops static (Geert Uytterhoeven)
- pvqspinlock: Convert fields of 'enum vcpu_state' to uppercase
(Qiuxu Zhuo)
- iio: magnetometer: Fix if () scoped_guard() formatting (Stephen
Rothwell)
- rtmutex: Fix misleading comment (Peter Zijlstra)
- percpu-rw-semaphores: Fix grammar in percpu-rw-semaphore.rst (Xiu
Jianfeng)"
* tag 'locking-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (29 commits)
locking/Documentation: Fix grammar in percpu-rw-semaphore.rst
iio: magnetometer: fix if () scoped_guard() formatting
rust: helpers: Avoid raw_spin_lock initialization for PREEMPT_RT
kcsan, seqlock: Fix incorrect assumption in read_seqbegin()
seqlock, treewide: Switch to non-raw seqcount_latch interface
kcsan, seqlock: Support seqcount_latch_t
time/sched_clock: Broaden sched_clock()'s instrumentation coverage
time/sched_clock: Swap update_clock_read_data() latch writes
locking/atomic/x86: Use ALT_OUTPUT_SP() for __arch_{,try_}cmpxchg64_emu()
locking/atomic/x86: Use ALT_OUTPUT_SP() for __alternative_atomic64()
cleanup: Add conditional guard helper
cleanup: Adjust scoped_guard() macros to avoid potential warning
locking/osq_lock: Use atomic_try_cmpxchg_release() in osq_unlock()
cleanup: Remove address space of returned pointer
locking/rtmutex: Fix misleading comment
locking/rt: Annotate unlock followed by lock for sparse.
locking/rt: Add sparse annotation for RCU.
locking/rt: Remove one __cond_lock() in RT's spin_trylock_irqsave()
locking/rt: Add sparse annotation PREEMPT_RT's sleeping locks.
locking/pvqspinlock: Convert fields of 'enum vcpu_state' to uppercase
...
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|
git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs multigrain timestamps from Christian Brauner:
"This is another try at implementing multigrain timestamps. This time
with significant help from the timekeeping maintainers to reduce the
performance impact.
Thomas provided a base branch that contains the required timekeeping
interfaces for the VFS. It serves as the base for the multi-grain
timestamp work:
- Multigrain timestamps allow the kernel to use fine-grained
timestamps when an inode's attributes is being actively observed
via ->getattr(). With this support, it's possible for a file to get
a fine-grained timestamp, and another modified after it to get a
coarse-grained stamp that is earlier than the fine-grained time. If
this happens then the files can appear to have been modified in
reverse order, which breaks VFS ordering guarantees.
To prevent this, a floor value is maintained for multigrain
timestamps. Whenever a fine-grained timestamp is handed out, record
it, and when later coarse-grained stamps are handed out, ensure
they are not earlier than that value. If the coarse-grained
timestamp is earlier than the fine-grained floor, return the floor
value instead.
The timekeeper changes add a static singleton atomic64_t into
timekeeper.c that is used to keep track of the latest fine-grained
time ever handed out. This is tracked as a monotonic ktime_t value
to ensure that it isn't affected by clock jumps. Because it is
updated at different times than the rest of the timekeeper object,
the floor value is managed independently of the timekeeper via a
cmpxchg() operation, and sits on its own cacheline.
Two new public timekeeper interfaces are added:
(1) ktime_get_coarse_real_ts64_mg() fills a timespec64 with the
later of the coarse-grained clock and the floor time
(2) ktime_get_real_ts64_mg() gets the fine-grained clock value,
and tries to swap it into the floor. A timespec64 is filled
with the result.
- The VFS has always used coarse-grained timestamps when updating the
ctime and mtime after a change. This has the benefit of allowing
filesystems to optimize away a lot metadata updates, down to around
1 per jiffy, even when a file is under heavy writes.
Unfortunately, this has always been an issue when we're exporting
via NFSv3, which relies on timestamps to validate caches. A lot of
changes can happen in a jiffy, so timestamps aren't sufficient to
help the client decide when to invalidate the cache. Even with
NFSv4, a lot of exported filesystems don't properly support a
change attribute and are subject to the same problems with
timestamp granularity. Other applications have similar issues with
timestamps (e.g backup applications).
If we were to always use fine-grained timestamps, that would
improve the situation, but that becomes rather expensive, as the
underlying filesystem would have to log a lot more metadata
updates.
This adds a way to only use fine-grained timestamps when they are
being actively queried. Use the (unused) top bit in
inode->i_ctime_nsec as a flag that indicates whether the current
timestamps have been queried via stat() or the like. When it's set,
we allow the kernel to use a fine-grained timestamp iff it's
necessary to make the ctime show a different value.
This solves the problem of being able to distinguish the timestamp
between updates, but introduces a new problem: it's now possible
for a file being changed to get a fine-grained timestamp. A file
that is altered just a bit later can then get a coarse-grained one
that appears older than the earlier fine-grained time. This
violates timestamp ordering guarantees.
This is where the earlier mentioned timkeeping interfaces help. A
global monotonic atomic64_t value is kept that acts as a timestamp
floor. When we go to stamp a file, we first get the latter of the
current floor value and the current coarse-grained time. If the
inode ctime hasn't been queried then we just attempt to stamp it
with that value.
If it has been queried, then first see whether the current coarse
time is later than the existing ctime. If it is, then we accept
that value. If it isn't, then we get a fine-grained time and try to
swap that into the global floor. Whether that succeeds or fails, we
take the resulting floor time, convert it to realtime and try to
swap that into the ctime.
We take the result of the ctime swap whether it succeeds or fails,
since either is just as valid.
Filesystems can opt into this by setting the FS_MGTIME fstype flag.
Others should be unaffected (other than being subject to the same
floor value as multigrain filesystems)"
* tag 'vfs-6.13.mgtime' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
fs: reduce pointer chasing in is_mgtime() test
tmpfs: add support for multigrain timestamps
btrfs: convert to multigrain timestamps
ext4: switch to multigrain timestamps
xfs: switch to multigrain timestamps
Documentation: add a new file documenting multigrain timestamps
fs: add percpu counters for significant multigrain timestamp events
fs: tracepoints around multigrain timestamp events
fs: handle delegated timestamps in setattr_copy_mgtime
timekeeping: Add percpu counter for tracking floor swap events
timekeeping: Add interfaces for handling timestamps with a floor value
fs: have setattr_copy handle multigrain timestamps appropriately
fs: add infrastructure for multigrain timestamps
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hrtimer_init_on_stack() is now unused. Delete it.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/510ce0d2944c4a382ea51e51d03dcfb73ba0f4f7.1730386209.git.namcao@linutronix.de
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hrtimer_setup() and hrtimer_setup_on_stack() take the callback function
pointer as argument and initialize the timer completely.
Replace the hrtimer_init*() variants and the open coded initialization of
hrtimer::function with the new setup mechanism.
Switch to use the new functions.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/2bae912336103405adcdab96b88d3ea0353b4228.1730386209.git.namcao@linutronix.de
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hrtimer_init_sleeper_on_stack() is now unused. Delete it.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/52549846635c0b3a2abf82101f539efdabcd9778.1730386209.git.namcao@linutronix.de
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hrtimer_setup_sleeper_on_stack() replaces hrtimer_init_sleeper_on_stack()
to keep the naming convention consistent.
Convert the usage sites over to it. The conversion was done with
Coccinelle.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/299c07f0f96af8ab3a7631b47b6ca22b06b20577.1730386209.git.namcao@linutronix.de
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The hrtimer_init*() API is replaced by hrtimer_setup*() variants to
initialize the timer including the callback function at once.
hrtimer_init_sleeper_on_stack() does not need user to setup the callback
function separately, so a new variant would not be strictly necessary.
Nonetheless, to keep the naming convention consistent, introduce
hrtimer_setup_sleeper_on_stack(). hrtimer_init_on_stack() will be removed
once all users are converted.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/7b5e18e6dd0ace9eaa211201528cb9dc23752454.1730386209.git.namcao@linutronix.de
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To initialize hrtimer on stack, hrtimer_init_on_stack() needs to be called
and also hrtimer::function must be set. This is error-prone and awkward to
use.
Introduce hrtimer_setup_on_stack() which does both of these things, so that
users of hrtimer can be simplified.
The new setup function also has a sanity check for the provided function
pointer. If NULL, a warning is emitted and a dummy callback installed.
hrtimer_init_on_stack() will be removed as soon as all of its users have
been converted to the new function.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/4b05e2ab3a82c517adf67fabc0f0cd8fe118b97c.1730386209.git.namcao@linutronix.de
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To initialize hrtimer, hrtimer_init() needs to be called and also
hrtimer::function must be set. This is error-prone and awkward to use.
Introduce hrtimer_setup() which does both of these things, so that users of
hrtimer can be simplified.
The new setup function also has a sanity check for the provided function
pointer. If NULL, a warning is emitted and a dummy callback installed.
hrtimer_init() will be removed as soon as all of its users have been
converted to the new function.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/5057c1ddbfd4b92033cd93d37fe38e6b069d5ba6.1730386209.git.namcao@linutronix.de
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hrtimer_init*_on_stack() is not covered by tracing when
CONFIG_DEBUG_OBJECTS_TIMERS=y.
Rework the functions similar to hrtimer_init() and hrtimer_init_sleeper()
so that the hrtimer_init() tracepoint is unconditionally available.
The rework makes hrtimer_init_sleeper() unused. Delete it.
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/74528e8abf2bb96e8bee85ffacbf14e15cf89f0d.1730386209.git.namcao@linutronix.de
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The timer and hrtimer soft interrupts are raised in hard interrupt
context. With threaded interrupts force enabled or on PREEMPT_RT this leads
to waking the ksoftirqd for the processing of the soft interrupt.
ksoftirqd runs as SCHED_OTHER task which means it will compete with other
tasks for CPU resources. This can introduce long delays for timer
processing on heavy loaded systems and is not desired.
Split the TIMER_SOFTIRQ and HRTIMER_SOFTIRQ processing into a dedicated
timers thread and let it run at the lowest SCHED_FIFO priority.
Wake-ups for RT tasks happen from hardirq context so only timer_list timers
and hrtimers for "regular" tasks are processed here. The higher priority
ensures that wakeups are performed before scheduling SCHED_OTHER tasks.
Using a dedicated variable to store the pending softirq bits values ensure
that the timer are not accidentally picked up by ksoftirqd and other
threaded interrupts.
It shouldn't be picked up by ksoftirqd since it runs at lower priority.
However if ksoftirqd is already running while a timer fires, then ksoftird
will be PI-boosted due to the BH-lock to ktimer's priority.
The timer thread can pick up pending softirqs from ksoftirqd but only
if the softirq load is high. It is not be desired that the picked up
softirqs are processed at SCHED_FIFO priority under high softirq load
but this can already happen by a PI-boost by a force-threaded interrupt.
[ frederic@kernel.org: rcutorture.c fixes, storm fix by introduction of
local_timers_pending() for tick_nohz_next_event() ]
[ junxiao.chang@intel.com: Ensure ktimersd gets woken up even if a
softirq is currently served. ]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org> [rcutorture]
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241106150419.2593080-4-bigeasy@linutronix.de
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Raising the timer soft interrupt is always done from hard interrupt
context, so it can be reduced to just setting the TIMER soft interrupt
flag. The soft interrupt will be invoked on return from interrupt.
Use therefore __raise_softirq_irqoff() to raise the TIMER soft interrupt,
which is a trivial optimization.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241106150419.2593080-3-bigeasy@linutronix.de
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Raising the hrtimer soft interrupt is always done from hard interrupt
context, so it can be reduced to just setting the HRTIMER soft interrupt
flag. The soft interrupt will be invoked on return from interrupt.
Use therefore __raise_softirq_irqoff() to raise the HRTIMER soft interrupt,
which is a trivial optimization.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241106150419.2593080-2-bigeasy@linutronix.de
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Now that the SIG_IGN problem is solved in the core code, the alarmtimer
callbacks do not require a return value anymore.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241105064214.318837272@linutronix.de
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Now that ignored posix timer signals are requeued and the timers are
rearmed on signal delivery the workaround to keep such timers alive and
self rearm them is not longer required.
Remove the unused alarm timer parts.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064214.252443020@linutronix.de
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Now that ignored posix timer signals are requeued and the timers are
rearmed on signal delivery the workaround to keep such timers alive and
self rearm them is not longer required.
Remove the relevant hacks and the not longer required return values from
the related functions. The alarm timer workarounds will be cleaned up in a
separate step.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064214.187239060@linutronix.de
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Queue posixtimers which have their signal ignored on the ignored list:
1) When the timer fires and the signal has SIG_IGN set
2) When SIG_IGN is installed via sigaction() and a timer signal
is already queued
This only happens when the signal is for a valid timer, which delivered the
signal in periodic mode. One-shot timer signals are correctly dropped.
Due to the lock order constraints (sighand::siglock nests inside
timer::lock) the signal code cannot access any of the timer fields which
are relevant to make this decision, e.g. timer::it_status.
This is addressed by establishing a protection scheme which requires to
lock both locks on the timer side for modifying decision fields in the
timer struct and therefore makes it possible for the signal delivery to
evaluate with only sighand:siglock being held:
1) Move the NULLification of timer->it_signal into the sighand::siglock
protected section of timer_delete() and check timer::it_signal in the
code path which determines whether the signal is dropped or queued on
the ignore list.
This ensures that a deleted timer cannot be moved onto the ignore
list, which would prevent it from being freed on exit() as it is not
longer in the process' posix timer list.
If the timer got moved to the ignored list before deletion then it is
removed from the ignored list under sighand lock in timer_delete().
2) Provide a new timer::it_sig_periodic flag, which gets set in the
signal queue path with both timer and sighand locks held if the timer
is actually in periodic mode at expiry time.
The ignore list code checks this flag under sighand::siglock and drops
the signal when it is not set.
If it is set, then the signal is moved to the ignored list independent
of the actual state of the timer.
When the signal is un-ignored later then the signal is moved back to
the signal queue. On signal delivery the posix timer side decides
about dropping the signal if the timer was re-armed, dis-armed or
deleted based on the signal sequence counter check.
If the thread/process exits then not yet delivered signals are
discarded which means the reference of the timer containing the
sigqueue is dropped and frees the timer.
This is way cheaper than requiring all code paths to lock
sighand::siglock of the target thread/process on any modification of
timer::it_status or going all the way and removing pending signals
from the signal queues on every rearm, disarm or delete operation.
So the protection scheme here is that on the timer side both timer::lock
and sighand::siglock have to be held for modifying
timer::it_signal
timer::it_sig_periodic
which means that on the signal side holding sighand::siglock is enough to
evaluate these fields.
In posixtimer_deliver_signal() holding timer::lock is sufficient to do the
sequence validation against timer::it_signal_seq because a concurrent
expiry is waiting on timer::lock to be released.
This completes the SIG_IGN handling and such timers are not longer self
rearmed which avoids pointless wakeups.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064214.120756416@linutronix.de
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To handle posix timer signals on sigaction(SIG_IGN) properly, the timers
will be queued on a separate ignored list.
Add the necessary cleanup code for timer_delete() and exit_itimers().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064213.987530588@linutronix.de
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The posix timer signal handling uses siginfo::si_sys_private for handling
the sequence counter check. That indirection is not longer required and the
sequence count value at signal queueing time can be stored in struct
k_itimer itself.
This removes the requirement of treating siginfo::si_sys_private special as
it's now always zero as the kernel does not touch it anymore.
Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Link: https://lore.kernel.org/all/20241105064213.852619866@linutronix.de
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To cure the SIG_IGN handling for posix interval timers, the preallocated
sigqueue needs to be embedded into struct k_itimer to prevent life time
races of all sorts.
Now that the prerequisites are in place, embed the sigqueue into struct
k_itimer and fixup the relevant usage sites.
Aside of preparing for proper SIG_IGN handling, this spares an extra
allocation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064213.719695194@linutronix.de
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In preparation for handling ignored posix timer signals correctly and
embedding the sigqueue struct into struct k_itimer, hand down a pointer to
the sigqueue struct into posix_timer_deliver_signal() instead of just
having a boolean flag.
No functional change.
Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Link: https://lore.kernel.org/all/20241105064213.652658158@linutronix.de
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To handle posix timers which have their signal ignored via SIG_IGN properly
it is required to requeue a ignored signal for delivery when SIG_IGN is
lifted so the timer gets rearmed.
Split the required code out of send_sigqueue() so it can be reused in
context of sigaction().
While at it rename send_sigqueue() to posixtimer_send_sigqueue() so its
clear what this is about.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064213.586453412@linutronix.de
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instead of re-evaluating the signal delivery mode everywhere.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064213.519086500@linutronix.de
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To cure the SIG_IGN handling for posix interval timers, the preallocated
sigqueue needs to be embedded into struct k_itimer to prevent life time
races of all sorts.
To make that work correctly it needs reference counting so that timer
deletion does not free the timer prematuraly when there is a signal queued
or delivered concurrently.
Add a rcuref to the posix timer part.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20241105064213.304756440@linutronix.de
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