linux.git/kernel/time/timekeeping.c, branch v7.2-rc1

timekeeping: Register default clocksource before taking tk_core.lock

2026-06-17T14:55:26+00:00

Commit f24df84cbe05 ("time/jiffies: Register jiffies clocksource before
usage") moved the jiffies clocksource registration into
clocksource_default_clock(), so that it is registered lazily on the first
call. __clocksource_register() acquires clocksource_mutex, but the first
caller is timekeeping_init(), which invokes clocksource_default_clock()
while holding tk_core.lock, a raw spinlock.

Acquiring a sleeping mutex while holding a raw spinlock is invalid.

The default clocksource only has to be registered before
tk_setup_internals() consumes its mult/shift/maxadj. Neither
clocksource_default_clock(), the ->enable() callback, nor the registration
itself need tk_core.lock, so fetch and enable the clock before acquiring
the lock. This preserves the "register before usage" ordering while
keeping clocksource_mutex out of the raw spinlock section.

clocksource_default_clock() has a second caller,
clocksource_done_booting(), which invokes it with clocksource_mutex already
held. That path avoids a recursive lock because timekeeping_init() has
already run and set cs_jiffies_registered, so the registration is skipped
there. This change does not alter that; it only fixes the invalid wait
context in timekeeping_init().

Fixes: f24df84cbe05 ("time/jiffies: Register jiffies clocksource before usage")
Signed-off-by: Mikhail Gavrilov 
Signed-off-by: Thomas Gleixner 
Reported-by: Breno Leitao 
Reported-by: Oleg Nesterov 
Reviewed-by: Breno Leitao 
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260616070914.65818-1-mikhail.v.gavrilov@gmail.com

timekeeping: Add clocksource read_snapshot() method and hw_cycles to snapshot

2026-06-04T09:04:18+00:00

Add a read_snapshot() callback to struct clocksource which returns the
derived clocksource value while also providing the underlying hardware
counter reading and the related clocksource ID.

This allows ktime_get_snapshot_id() to populate new hw_cycles and hw_csid
fields in struct system_time_snapshot.

For clocksources that are derived from an underlying counter (e.g., Hyper-V
TSC page scales TSC to 10MHz, kvmclock scales TSC to 1GHz), this provides
atomic access to both the derived value needed for timekeeping
calculations, and the raw hardware counter needed by consumers like KVM's
master clock and the vmclock PTP driver.

[ tglx: Reworked it slightly ]

Signed-off-by: David Woodhouse 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Jacob Keller 
Assisted-by: Kiro:claude-opus-4.6-1m
Link: https://patch.msgid.link/20260526230635.136914-1-dwmw2@infradead.org
Link: https://patch.msgid.link/20260529195558.202568489@kernel.org

timekeeping: Add support for AUX clock cross timestamping

2026-06-04T09:04:18+00:00

Now that all prerequisites are in place add the final support for AUX
clocks in get_device_system_crosststamp(), which enables the PTP layer to
support hardware cross timestamps with a new IOTCL.

Signed-off-by: Thomas Gleixner 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Thomas Weißschuh 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195558.097464513@kernel.org

timekeeping: Prepare for cross timestamps on arbitrary clock IDs

2026-06-04T09:04:17+00:00

PTP device system crosstime stamps support only CLOCK_REALTIME, which is
meaningless for AUX clocks. The PTP core hands in the clock ID already, so
prepare the core code to honor it.

 - Add a new sys_systime field to struct system_device_crosststamp which
   aliases the sys_realtime field. Once all users are converted
   sys_realtime can be removed.

 - Prepare get_device_system_crosststamp() and the related code for it by
   switching to sys_systime and providing the initial changes to utilize
   different time keepers.

No functional change intended.

Signed-off-by: Thomas Gleixner 
Tested-by: David Woodhouse 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Thomas Weißschuh 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195557.846634842@kernel.org

timekeeping: Add system_counterval_t to struct system_device_crosststamp

2026-06-04T09:04:16+00:00

An upcoming extension to the PTP IOCTL requires to return the system counter
value and the clocksource ID to user space. get_device_system_crosststamp() has
this information already.

Extend struct system_device_crosststamp with a system_counterval_t member
and fill in the data.

Signed-off-by: Thomas Gleixner 
Tested-by: David Woodhouse 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195557.429406675@kernel.org

timekeeping: Add CLOCK_AUX support for ktime_get_snapshot_id()

2026-06-04T09:04:16+00:00

Now that all users are converted it's possible to enable snapshotting of
CLOCK_AUX time. The underlying clocksource is the same as for all other
CLOCK variants.

Signed-off-by: Thomas Gleixner 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Thomas Weißschuh 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195557.380601005@kernel.org

timekeeping: Remove system_time_snapshot::real/boot/raw

2026-06-04T09:04:16+00:00

All users are converted over to ktime_get_snapshot_id() and
system_time_snapshot::systime and ::monoraw.

Remove the leftovers.

Signed-off-by: Thomas Gleixner 
Tested-by: David Woodhouse 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Thomas Weißschuh 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195557.330029635@kernel.org

timekeeping: Use system_time_snapshot::systime/monoraw instead of ::real/raw

2026-06-02T09:39:57+00:00

system_time_snapshot::systime provides the same information as
system_time_snapshot::real when the snapshot was taken with
ktime_get_snapshot_id(CLOCK_REALTIME).

Convert the history interpolation over to use 'systime' and 'monoraw' as
'real/raw' are going away once all users are converted.

As a side effect this is the first step to support CLOCK_AUX with
get_device_crosstime_stamp() and the history interpolation.

Signed-off-by: Thomas Gleixner 
Tested-by: David Woodhouse 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Thomas Weißschuh 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195557.024415766@kernel.org

timekeeping: Provide ktime_get_snapshot_id()

2026-06-02T09:39:57+00:00

ktime_get_snapshot() provides a snapshot of the underlying clocksource
counter value and the corresponding CLOCK_MONOTONIC_RAW, CLOCK_REALTIME and
CLOCK_BOOTTIME timestamps.

There is no usage of CLOCK_REALTIME and CLOCK_BOOTTIME at the same time and
CLOCK_BOOTTIME support was just added for the ARM64 KVM tracing mechanism,
which needs CLOCK_BOOTTIME and the underlying clocksource counter value.

ktime_get_snapshot() is also not suitable for usage with CLOCK_AUX, but
that's a prerequisite to support PTP hardware timestamping for CLOCK_AUX
steering.

As a first step, rename ktime_get_snapshot() to ktime_get_snapshot_id(),
which now takes a clockid argument to select the clock which needs to be
captured. The result is stored in system_time_snapshot::systime, which will
replace the system_time_snapshot::real/boot members once all usage sites
have been converted.

ktime_get_snapshot() is a simple wrapper which hands in CLOCK_REALTIME as
clockid argument for the conversion period. That means CLOCK_REALTIME is
now captured twice, but that redunancy is only temporary.

As all usage sites of struct system_time_snapshot has to be updated anyway,
rename the 'raw' member to 'monoraw' for clarity.

No functional change vs. current users of ktime_get_snapshot()

Signed-off-by: Thomas Gleixner 
Tested-by: David Woodhouse 
Tested-by: Arthur Kiyanovski 
Reviewed-by: David Woodhouse 
Reviewed-by: Thomas Weißschuh 
Reviewed-by: Jacob Keller 
Link: https://patch.msgid.link/20260529195556.971591633@kernel.org

Merge tag 'v7.0-rc4' into timers/core, to resolve conflict

2026-03-21T07:02:36+00:00

Resolve conflict between this change in the upstream kernel:

  4c652a47722f ("rseq: Mark rseq_arm_slice_extension_timer() __always_inline")

... and this pending change in timers/core:

  0e98eb14814e ("entry: Prepare for deferred hrtimer rearming")

Signed-off-by: Ingo Molnar