[SourceKit] Resolve a nondeterministic deadlock in SourceKit while cancelling #42258
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…ncelling This fixes a race-conditioned deadlock which could occur while cancelling SourceKit AST build request We have one thread that claimed `CancellationRequestCallbackMtx` in `SwiftASTConsumer::requestCancellation` and wants to claim `ConsumersAndResultMtx` in `ASTBuildOperation::requestConsumerCancellation` Another thread claimed `ConsumersAndResultMtx` in `ASTBuildOperation::schedule` and now wants to claim `CancellationRequestCallbackMtx` in `SwiftASTConsumer::removeCancellationRequestCallback`. In both cases we could actually release one lock before claiming the other. Fixes rdar://90870793
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bnbarham
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Apr 8, 2022
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| if (Result) { | ||
| informConsumer(Consumer); | ||
| return true; | ||
| } |
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Ideally this would be outside the lock as well - maybe check !Result here and then the same check outside the lock to either inform/add cancellation?
bnbarham
approved these changes
May 18, 2022
This was referenced May 19, 2022
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This fixes a race-conditioned deadlock which could occur while cancelling SourceKit AST build request
We have one thread that claimed
CancellationRequestCallbackMtxinSwiftASTConsumer::requestCancellationand wants to claimConsumersAndResultMtxinASTBuildOperation::requestConsumerCancellationAnother thread claimed
ConsumersAndResultMtxinASTBuildOperation::scheduleand now wants to claimCancellationRequestCallbackMtxinSwiftASTConsumer::removeCancellationRequestCallback.In both cases we could actually release one lock before claiming the other.
Fixes rdar://90870793