Re: [lttng-dev] [PATCH v2 00/12] Add support for TSAN to liburcu

["Ondřej Surý via lttng-dev" <lttng-dev@lists.lttng.org>]

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@sury.org> (He/Him)

> On 7. 6. 2023, at 20:54, Olivier Dion <odion@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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