Fix crash in task groups due to atomics. #40252
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A `compare_exchange_weak` can spuriously return false, regardless of whether a concurrent access happened. This was causing a null-pointer dereference in TaskGroupImpl::poll in a narrow circumstance. The dereference failure only appears when using the `arm64` slice of the runtime library, since Clang will use `ldxr/stxr` for synchronization on such targets. The weak form does not retry on a spurious failure, but the strong version will. resolves rdar://84192672
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@swift-ci please smoke test and merge |
ktoso
approved these changes
Nov 19, 2021
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A
compare_exchange_weakcan spuriously return false, regardless ofwhether a concurrent access happened. This was causing a null-pointer
dereference in TaskGroupImpl::poll in a narrow circumstance.
The dereference failure only appears when using the
arm64slice of the runtime library, since Clang will use
ldxr/stxrforsynchronization on such targets. The weak form does not retry on a
spurious failure, but the strong version will.
resolves rdar://84192672