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

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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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2 changed files with 3 additions and 5 deletions
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6
Python/lock.c
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@ -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);
}