[Concurrency] Fix races/overflows in TaskGroup implementation. #81814
+195
−107
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@swift-ci please test |
ktoso
reviewed
May 28, 2025
| @@ -378,7 +378,7 @@ public func _unsafeInheritExecutor_withThrowingDiscardingTaskGroup<GroupResult>( | |||
| discardResults: true | |||
| ) | |||
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| let _group = Builtin.createTaskGroupWithFlags(flags, GroupResult.self) | |||
| let _group = Builtin.createTaskGroupWithFlags(flags, Void.self) | |||
ktoso
reviewed
May 28, 2025
| old.status, old.completingPendingReadyWaiting(this).status, | ||
| /*success*/ std::memory_order_relaxed, | ||
| /*failure*/ std::memory_order_relaxed); | ||
| /*failure*/ std::memory_order_relaxed)) { | ||
| } // Loop until the compare_exchange succeeds |
ktoso
reviewed
May 28, 2025
| @@ -1796,77 +1803,81 @@ reevaluate_if_taskgroup_has_results:; | |||
| auto waitHead = waitQueue.load(std::memory_order_acquire); | |||
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| // ==== 2) Ready task was polled, return with it immediately ----------------- | |||
| if (assumed.readyTasks(this)) { | |||
| while (assumed.readyTasks(this)) { | |||
ktoso
approved these changes
May 28, 2025
statusCompletePendingReadyWaiting(), offer(), and poll() did a one-off compare_exchange_strong which could fail if the group was concurrently cancelled. Put these into loops so that they are retried when needed. DiscardingTaskGroup creation passed the group result type as the task result type. waitAll() would then use the group result type when collecting task results. Since the task result type is always Void in this case, this would overflow the result buffer if the group result type was larger. This often works as it writes into the free space of the task allocator, but can crash if it happens to be at the end of a page or the group result type is particularly large. rdar://151663730
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@swift-ci please test |
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Looks like macOS hit the issue fixed by #81830 and everything was good otherwise. Retrying. |
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@swift-ci please smoke test macos platform |
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statusCompletePendingReadyWaiting(), offer(), and poll() did a one-off compare_exchange_strong which could fail if the group was concurrently cancelled. Put these into loops so that they are retried when needed.
DiscardingTaskGroup creation passed the group result type as the task result type. waitAll() would then use the group result type when collecting task results. Since the task result type is always Void in this case, this would overflow the result buffer if the group result type was larger. This often works as it writes into the free space of the task allocator, but can crash if it happens to be at the end of a page or the group result type is particularly large.
rdar://151663730