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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.
This commit is contained in:
mpage 2024-04-17 10:19:28 -07:00 committed by GitHub
parent b6c62c79e7
commit 0d29302155
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GPG Key ID: B5690EEEBB952194
2 changed files with 3 additions and 5 deletions
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6
Python/lock.c
View File

@ -472,7 +472,7 @@ _PyRWMutex_Unlock(_PyRWMutex *rwmutex)
void _PySeqLock_LockWrite(_PySeqLock *seqlock) 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); uint32_t prev = _Py_atomic_load_uint32_relaxed(&seqlock->sequence);
while (1) { while (1) {
if (SEQLOCK_IS_UPDATING(prev)) { if (SEQLOCK_IS_UPDATING(prev)) {
@ -492,14 +492,14 @@ void _PySeqLock_LockWrite(_PySeqLock *seqlock)
void _PySeqLock_AbandonWrite(_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)); assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq); _Py_atomic_store_uint32(&seqlock->sequence, new_seq);
} }
void _PySeqLock_UnlockWrite(_PySeqLock *seqlock) 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)); assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq); _Py_atomic_store_uint32(&seqlock->sequence, new_seq);
} }

2
Tools/tsan/suppressions_free_threading.txt
View File

@ -26,7 +26,6 @@ race:_PyObject_GC_IS_SHARED
race:_PyObject_GC_SET_SHARED race:_PyObject_GC_SET_SHARED
race:_PyObject_GC_TRACK race:_PyObject_GC_TRACK
race:_PyType_HasFeature race:_PyType_HasFeature
race:_PyType_Lookup
race:assign_version_tag race:assign_version_tag
race:compare_unicode_unicode race:compare_unicode_unicode
race:delitem_common race:delitem_common
@ -47,4 +46,3 @@ race:set_inheritable
race:start_the_world race:start_the_world
race:tstate_set_detached race:tstate_set_detached
race:unicode_hash race:unicode_hash
race:update_cache_gil_disabled