diff options
Diffstat (limited to 'Python/lock.c')
| -rw-r--r-- | Python/lock.c | 26 |
1 files changed, 15 insertions, 11 deletions
diff --git a/Python/lock.c b/Python/lock.c index 7c6a517..57675fe 100644 --- a/Python/lock.c +++ b/Python/lock.c @@ -514,6 +514,7 @@ void _PySeqLock_LockWrite(_PySeqLock *seqlock) } else if (_Py_atomic_compare_exchange_uint32(&seqlock->sequence, &prev, prev + 1)) { // We've locked the cache + _Py_atomic_fence_release(); break; } else { @@ -547,28 +548,31 @@ uint32_t _PySeqLock_BeginRead(_PySeqLock *seqlock) return sequence; } -uint32_t _PySeqLock_EndRead(_PySeqLock *seqlock, uint32_t previous) +int _PySeqLock_EndRead(_PySeqLock *seqlock, uint32_t previous) { - // Synchronize again and validate that the entry hasn't been updated - // while we were readying the values. - if (_Py_atomic_load_uint32_acquire(&seqlock->sequence) == previous) { + // gh-121368: We need an explicit acquire fence here to ensure that + // this load of the sequence number is not reordered before any loads + // within the read lock. + _Py_atomic_fence_acquire(); + + if (_Py_atomic_load_uint32_relaxed(&seqlock->sequence) == previous) { return 1; - } + } - _Py_yield(); - return 0; + _Py_yield(); + return 0; } -uint32_t _PySeqLock_AfterFork(_PySeqLock *seqlock) +int _PySeqLock_AfterFork(_PySeqLock *seqlock) { // Synchronize again and validate that the entry hasn't been updated // while we were readying the values. - if (SEQLOCK_IS_UPDATING(seqlock->sequence)) { + if (SEQLOCK_IS_UPDATING(seqlock->sequence)) { seqlock->sequence = 0; return 1; - } + } - return 0; + return 0; } #undef PyMutex_Lock |