[lttng-dev] [PATCH v2 00/12] Add support for TSAN to liburcu
Ondřej Surý
ondrej at sury.org
Wed Jun 7 15:04:26 EDT 2023
Olivier,
is this somewhere in Gerrit again, please? It’s much easier for us to pull the changes from git than cherry-pick patches from the mailing list.
Ondřej
--
Ondřej Surý <ondrej at sury.org> (He/Him)
> On 7. 6. 2023, at 20:54, Olivier Dion <odion at efficios.com> wrote:
>
> This patch set adds support for TSAN in liburcu.
>
> * Change since v1
>
> ** Adding CMM_SEQ_CST_FENCE memory order to the CMM memory model
>
> The C11 memory model is incompatible with the memory model used by liburcu,
> since the semantic of the C11 memory model is based on a happen-before
> (acquire/release) relationship of memory accesses, while liburcu is based on
> memory barriers and relaxed memory accesses.
>
> To circumvent this, a new memory order called CMM_SEQ_CST_FENCE is
> introduced. It implies a CMM_SEQ_CST while emitting a thread fence after the
> operation. Operations that were documented as emitting memory barriers
> before and after the operation are implemented now in term of this new memory
> order to keep compatibility.
>
> However, this model is redundant in some cases and the memory orders were
> changed internally in liburcu to simply use the CMM_SEQ_CST.
>
> ** Adding cmm_emit_legacy_smp_mb() to queue/stack APIs
>
> The queue/stack APIs document implicit memory barriers before or after
> operation. These are now optionally emitted only if
> CONFIG_RCU_EMIT_LEGACY_MB is defined in urcu/config.h or manually defined by
> the user before including liburcu. That way, users can opt-in even if the
> system headers were configured without this feature.
>
> However, users can not opt-out of that feature if configured by the system.
>
> * v1
>
> ** Here are the major changes
>
> - Usage of compiler atomic builtins is added to the uatomic API. This is
> required for TSAN to understand atomic memory accesses. If the compiler
> supports such builtins, they are used by default. User can opt-out and use
> the legacy implementation of the uatomic API by using the
> `--disable-atomic-builtins' configuration option.
>
> - The CMM memory model is introduced but yet formalized. It tries to be as
> close as possible to the C11 memory model while offering primitives such as
> cmm_smp_wmb(), cmm_smp_rmb() and cmm_mb() that can't be expressed in it.
> For example, cmm_mb() can be used for ordering memory accesses to MMIO
> devices, which is out of the scope of the C11 memory model.
>
> - The CMM annotation layer is a new public API that is highly experimental and
> not guaranteed to be stable at this stage. It serves the dual purpose of
> verifying local (intra-thread) relaxed atomic accesses ordering with a
> memory barrier and global (inter-thread) relaxed atomic accesses with a
> shared state. The second purpose is necessary for TSAN to understand memory
> accesses ordering since it does not fully support thread fence yet.
>
> ** CMM annotation example
>
> Consider the following pseudo-code of writer side in synchronize_rcu(). An
> acquire group is defined on the stack of the writer. Annotations are made
> onto the group to ensure ordering of relaxed memory accesses in reader_state()
> before the memory barrier at the end of synchronize_rcu(). It also helps TSAN
> to understand that the relaxed accesses in reader_state() act like acquire
> accesses because of the memory barrier in synchronize_rcu().
>
> In other words, the purpose of this annotation is to convert a group of
> load-acquire memory operations into load-relaxed memory operations followed by
> a single memory barrier. This highly benefits weakly ordered architectures by
> having a constant number of memory barriers instead of being linearly
> proportional to the number of loads. This does not benefit TSO
> architectures.
>
>
> Olivier Dion (12):
> configure: Add --disable-atomic-builtins option
> urcu/compiler: Use atomic builtins if configured
> urcu/arch/generic: Use atomic builtins if configured
> urcu/system: Use atomic builtins if configured
> urcu/uatomic: Add CMM memory model
> urcu-wait: Fix wait state load/store
> tests: Use uatomic for accessing global states
> benchmark: Use uatomic for accessing global states
> tests/unit/test_build: Quiet unused return value
> urcu/annotate: Add CMM annotation
> Add cmm_emit_legacy_smp_mb()
> tests: Add tests for checking race conditions
>
> README.md | 11 ++
> configure.ac | 39 ++++
> doc/uatomic-api.md | 3 +-
> include/Makefile.am | 3 +
> include/urcu/annotate.h | 174 ++++++++++++++++++
> include/urcu/arch.h | 6 +
> include/urcu/arch/generic.h | 37 ++++
> include/urcu/compiler.h | 22 ++-
> include/urcu/config.h.in | 6 +
> include/urcu/static/lfstack.h | 25 ++-
> include/urcu/static/pointer.h | 40 ++--
> include/urcu/static/rculfqueue.h | 14 +-
> include/urcu/static/rculfstack.h | 8 +-
> include/urcu/static/urcu-bp.h | 12 +-
> include/urcu/static/urcu-common.h | 8 +-
> include/urcu/static/urcu-mb.h | 11 +-
> include/urcu/static/urcu-memb.h | 26 ++-
> include/urcu/static/urcu-qsbr.h | 29 ++-
> include/urcu/static/wfcqueue.h | 68 +++----
> include/urcu/static/wfqueue.h | 9 +-
> include/urcu/static/wfstack.h | 24 ++-
> include/urcu/system.h | 21 +++
> include/urcu/uatomic.h | 63 ++++++-
> include/urcu/uatomic/builtins-generic.h | 170 +++++++++++++++++
> include/urcu/uatomic/builtins.h | 79 ++++++++
> include/urcu/uatomic/generic.h | 234 ++++++++++++++++++++++++
> src/rculfhash.c | 92 ++++++----
> src/urcu-bp.c | 17 +-
> src/urcu-pointer.c | 9 +-
> src/urcu-qsbr.c | 31 +++-
> src/urcu-wait.h | 15 +-
> src/urcu.c | 24 ++-
> tests/benchmark/Makefile.am | 91 ++++-----
> tests/benchmark/common-states.c | 1 +
> tests/benchmark/common-states.h | 51 ++++++
> tests/benchmark/test_mutex.c | 32 +---
> tests/benchmark/test_perthreadlock.c | 32 +---
> tests/benchmark/test_rwlock.c | 32 +---
> tests/benchmark/test_urcu.c | 33 +---
> tests/benchmark/test_urcu_assign.c | 33 +---
> tests/benchmark/test_urcu_bp.c | 33 +---
> tests/benchmark/test_urcu_defer.c | 33 +---
> tests/benchmark/test_urcu_gc.c | 34 +---
> tests/benchmark/test_urcu_hash.c | 6 +-
> tests/benchmark/test_urcu_hash.h | 15 --
> tests/benchmark/test_urcu_hash_rw.c | 10 +-
> tests/benchmark/test_urcu_hash_unique.c | 10 +-
> tests/benchmark/test_urcu_lfq.c | 20 +-
> tests/benchmark/test_urcu_lfs.c | 20 +-
> tests/benchmark/test_urcu_lfs_rcu.c | 20 +-
> tests/benchmark/test_urcu_qsbr.c | 33 +---
> tests/benchmark/test_urcu_qsbr_gc.c | 34 +---
> tests/benchmark/test_urcu_wfcq.c | 22 +--
> tests/benchmark/test_urcu_wfq.c | 20 +-
> tests/benchmark/test_urcu_wfs.c | 22 +--
> tests/common/api.h | 12 +-
> tests/regression/rcutorture.h | 106 +++++++----
> tests/unit/test_build.c | 8 +-
> tests/unit/test_lfstack.c | 90 +++++++++
> tests/unit/test_wfcqueue.c | 119 ++++++++++++
> tests/unit/test_wfqueue.c | 91 +++++++++
> tests/unit/test_wfstack.c | 90 +++++++++
> 62 files changed, 1799 insertions(+), 684 deletions(-)
> create mode 100644 include/urcu/annotate.h
> create mode 100644 include/urcu/uatomic/builtins-generic.h
> create mode 100644 include/urcu/uatomic/builtins.h
> create mode 100644 tests/benchmark/common-states.c
> create mode 100644 tests/benchmark/common-states.h
> create mode 100644 tests/unit/test_lfstack.c
> create mode 100644 tests/unit/test_wfcqueue.c
> create mode 100644 tests/unit/test_wfqueue.c
> create mode 100644 tests/unit/test_wfstack.c
>
> --
> 2.40.1
>
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