[RELEASE] Userspace RCU 0.14.3 and 0.15.7

[RELEASE] Userspace RCU 0.14.3 and 0.15.7

[Mathieu Desnoyers via lttng-dev]

Hi,

I hereby announce the 0.14.3 and 0.15.7 bugfix releases for the
currently maintained Userspace RCU stable branches.

liburcu is a LGPLv2.1 userspace RCU (read-copy-update) library. This
data synchronization library provides read-side access which scales
linearly with the number of cores. It does so by allowing multiple
copies of a given data structure to live at the same time, and by
monitoring the data structure accesses to detect grace periods after
which memory reclamation is possible.

liburcu-cds provides efficient data structures based on RCU and
lock-free algorithms. Those structures include hash tables, queues,
stacks, and doubly-linked lists.

* Highlight

The most relevant fix in those releases is a fix for the memory
ordering of rcu_dereference() when used in code compiled without
_LGPL_SOURCE. The issue is that the load is non-volatile, non-atomic,
and lacks the relevant memory-order-consume semantic.

The fix is twofold:

1) A work-around in rcu_dereference_sym() which adds a cmm_smp_mb().
    This fixes memory ordering but not load atomicity.

2) Introduction of a new rcu_dereference_sym2() which fixes both
    atomicity and memory ordering. The macro now maps to this new
    symbol. The old symbol is preserved for backward compatibility.

There is also a change to the call-rcu worker to make sure the CPU
affinity is set earlier in the worker thread lifetime, eliminating
unwanted call RCU worker thread migration behaviors early in the
process lifetime (first ~2.5 seconds).

Changelog:

2026-09-11 Userspace RCU 0.15.7
         * call-rcu worker: set CPU affinity on first non-empty dequeue
         * Fix: leaky wfcq tests
         * Fix: test_build.c: Test output mismatch
         * Fix: workqueue leaks mutexes on FreeBSD
         * Fix: call-rcu leaks mutexes on FreeBSD
         * call_rcu: pin per-CPU worker at thread startup
         * urcu-pointer: Add rcu_dereference_sym2() taking the pointer address
         * urcu-pointer: Fix missing memory ordering in rcu_dereference_sym()

2026-09-11 Userspace RCU 0.14.3
         * call-rcu worker: set CPU affinity on first non-empty dequeue
         * Fix: leaky wfcq tests
         * Fix: test_build.c: Test output mismatch
         * Fix: workqueue leaks mutexes on FreeBSD
         * Fix: call-rcu leaks mutexes on FreeBSD
         * call_rcu: pin per-CPU worker at thread startup
         * urcu-pointer: Add rcu_dereference_sym2() taking the pointer address
         * urcu-pointer: Fix missing memory ordering in rcu_dereference_sym()

Project website: https://liburcu.org
Git repository: https://git.liburcu.org/userspace-rcu.git
-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com