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aaf3d47e53
- Futher cleanups for the POSIX timer exit/exec related code to simplify
the code flow and to make it more robust against future changes.
- Prevent tearing of timekeeper::ktime_sec which can be accessed without the
sequence count protection.
The timekeeper is updated by memcpy() with an uneven sequence count to
force readers into the retry path. On 64-bit machine the ktime_sec
member can be accessed atomically without the sequence count
protection. That is only correct when the update side memcpy()
guarantees atomicity at the 64-bit granularity. That's not guaranteed
due to debug options, compilers and instruction availability. If the
memcpy() does not provide the atomicity then the unprotected readers
can observe store tearing.
To prevent this write the ktime_sec member before the memcpy() so that
a non-atomic memcpy() will write the same data. A similar fix has been
done for the xtime_sec member, but the ktime_sec equivalent was missed.
- Prevent time64_to_tm() day truncation on 32-bit kernels
The function receives a 64-bit seconds value but stores the quotient of
the computation in a long, which truncates the result for large input
values. Cure this by using div_s64_rem() which stores the quotient in
s64 and only leaves the seconds-within-day reminder in a long, which is
guaranteed to fit. This fix comes with a corresponding kunit test to
prevent further mishaps.
- Mark data-racy accesses to the hrtimer_sleeper::task member.
The recent updates to KCSAN flagged these benign races. Annotate them
with new helper functions, convert all existing usage sites and mark
the task member private after that so that future users which fail to
use the helpers can be detected automatically.
- Address similar benign KCSAN flagged issues in the hrtimer, timer and
timer migration code.
- Fixes for a few selftest issues
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Merge tag 'timers-core-2026-10-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer core updates from Thomas Gleixner:
"Updates for the core timekeeping and timers subsystem:
- Futher cleanups for the POSIX timer exit/exec related code to
simplify the code flow and to make it more robust against future
changes.
- Prevent tearing of timekeeper::ktime_sec which can be accessed
without the sequence count protection.
The timekeeper is updated by memcpy() with an uneven sequence count
to force readers into the retry path. On 64-bit machine the
ktime_sec member can be accessed atomically without the sequence
count protection. That is only correct when the update side
memcpy() guarantees atomicity at the 64-bit granularity. That's not
guaranteed due to debug options, compilers and instruction
availability. If the memcpy() does not provide the atomicity then
the unprotected readers can observe store tearing.
To prevent this write the ktime_sec member before the memcpy() so
that a non-atomic memcpy() will write the same data. A similar fix
has been done for the xtime_sec member, but the ktime_sec
equivalent was missed.
- Prevent time64_to_tm() day truncation on 32-bit kernels
The function receives a 64-bit seconds value but stores the
quotient of the computation in a long, which truncates the result
for large input values. Cure this by using div_s64_rem() which
stores the quotient in s64 and only leaves the seconds-within-day
reminder in a long, which is guaranteed to fit. This fix comes with
a corresponding kunit test to prevent further mishaps.
- Mark data-racy accesses to the hrtimer_sleeper::task member.
The recent updates to KCSAN flagged these benign races. Annotate
them with new helper functions, convert all existing usage sites
and mark the task member private after that so that future users
which fail to use the helpers can be detected automatically.
- Address similar benign KCSAN flagged issues in the hrtimer, timer
and timer migration code.
- Fixes for a few selftest issues"
* tag 'timers-core-2026-10-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (26 commits)
selftests/timers: clocksource-switch: Fix unchecked open()/read()
selftests: timers: Measure the CPU timers on the clock they count
selftests: timers: Count what tick is worth in the drift estimate
time/kunit: Add time64_to_tm() case beyond 32-bit day count
time: Prevent time64_to_tm() day truncation on 32-bit
timekeeping: Use READ_ONCE/WRITE_ONCE() for ktime_sec to prevent tearing
timers/migration: Mark racy updates to tmigr_event::ignore field
timers: Mark racy updates to hlist_node::pprev field
hrtimer: Apply READ_ONCE() to lockless base->running loads
hrtimer: Mark the hrtimer_sleeper structure's ->task field __private
hrtimer: Update hrtimer_resolution only if value changes
futex: Use accessor for hrtimer_sleeper ->task field in requeue
rtmutex: Use accessor for hrtimer_sleeper ->task field
net: pktgen: Use accessor for hrtimer_sleeper ->task field
timers: Use accessor for hrtimer_sleeper ->task field in sleep_timeout.c
futex: Use accessor for hrtimer_sleeper ->task field in waitwake.c
io-uring/rw: Use accessor for hrtimer_sleeper ->task field
wait: Use accessor for hrtimer_sleeper ->task field
aio: Use accessor for hrtimer_sleeper ->task field
hrtimer: Mark data-racy accesses to hrtimer_sleeper ->task field
...
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|---|---|---|
| .. | ||
| core.c | ||
| futex.h | ||
| Makefile | ||
| pi.c | ||
| requeue.c | ||
| syscalls.c | ||
| waitwake.c | ||