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https://github.com/python/cpython/commit/0d29302155f49d4d5c7fa34a658ad5a97dd013a2
commit: 0d29302155f49d4d5c7fa34a658ad5a97dd013a2
branch: main
author: mpage <mpage@meta.com>
committer: DinoV <dinoviehland@gmail.com>
date: 2024-04-17T17:19:28Z
summary:

gh-117657: Quiet erroneous TSAN reports of data races in `_PySeqLock` (#117955)

Quiet erroneous TSAN reports of data races in `_PySeqLock`

TSAN reports a couple of data races between the compare/exchange in
`_PySeqLock_LockWrite` and the non-atomic loads in `_PySeqLock_{Abandon,Unlock}Write`.
This is another instance of TSAN incorrectly modeling failed compare/exchange
as a write instead of a load.

files:
M Python/lock.c
M Tools/tsan/suppressions_free_threading.txt

diff --git a/Python/lock.c b/Python/lock.c
index 7d1ead585dee6c..91c66df8fd9093 100644
--- a/Python/lock.c
+++ b/Python/lock.c
@@ -472,7 +472,7 @@ _PyRWMutex_Unlock(_PyRWMutex *rwmutex)

void _PySeqLock_LockWrite(_PySeqLock *seqlock)
{
- // lock the entry by setting by moving to an odd sequence number
+ // lock by moving to an odd sequence number
uint32_t prev = _Py_atomic_load_uint32_relaxed(&seqlock->sequence);
while (1) {
if (SEQLOCK_IS_UPDATING(prev)) {
@@ -492,14 +492,14 @@ void _PySeqLock_LockWrite(_PySeqLock *seqlock)

void _PySeqLock_AbandonWrite(_PySeqLock *seqlock)
{
- uint32_t new_seq = seqlock->sequence - 1;
+ uint32_t new_seq = _Py_atomic_load_uint32_relaxed(&seqlock->sequence) - 1;
assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq);
}

void _PySeqLock_UnlockWrite(_PySeqLock *seqlock)
{
- uint32_t new_seq = seqlock->sequence + 1;
+ uint32_t new_seq = _Py_atomic_load_uint32_relaxed(&seqlock->sequence) + 1;
assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq);
}
diff --git a/Tools/tsan/suppressions_free_threading.txt b/Tools/tsan/suppressions_free_threading.txt
index 6e2bdc1ea85cd6..80191d6c2484e6 100644
--- a/Tools/tsan/suppressions_free_threading.txt
+++ b/Tools/tsan/suppressions_free_threading.txt
@@ -26,7 +26,6 @@ race:_PyObject_GC_IS_SHARED
race:_PyObject_GC_SET_SHARED
race:_PyObject_GC_TRACK
race:_PyType_HasFeature
-race:_PyType_Lookup
race:assign_version_tag
race:compare_unicode_unicode
race:delitem_common
@@ -47,4 +46,3 @@ race:set_inheritable
race:start_the_world
race:tstate_set_detached
race:unicode_hash
-race:update_cache_gil_disabled

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