Eliminate a race condition in NSError bridging #3975
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Huge thanks to John for noting that 'consume' didn't provide the guarantees we wanted, and to Michael G. for getting a TSan build up and running to identify/verify this race. It's possible that this is overlay strict, and that we only need to look at the domain to ensure that the code and userInfo are visible. However, TSan seems to prefix the form in this patch, so we'll be more conservative for now. Fixes rdar://problem/27541751. (cherry picked from commit e07e887)
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@swift-ci please test |
| @@ -334,6 +332,10 @@ static id _swift_bridgeErrorToNSError_(SwiftError *errorObject) { | |||
| NSDictionary *userInfo = | |||
| swift_stdlib_getErrorUserInfoNSDictionary(value, type, witness); | |||
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| // Never produce an empty userInfo dictionary. | |||
| if (!userInfo) | |||
| userInfo = SWIFT_LAZY_CONSTANT(@{}); | |||
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Do we already do this somewhere else? We might want to factor this out into a static helper so there's only one global initializer for all empty dictionaries.
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I eliminated the other place I know about, but I do want to revisit this because on modern platforms we don't need the dispatch_once at all for empty collection literals.
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Looks good as a conservative fix. |
kateinoigakukun
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Aug 31, 2022
[pull] swiftwasm from main
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What's in this pull request?
This PR eliminates a race condition in NSError bridging, where we could end up observing uninitialized the userInfo dictionary in an _SwiftNativeNSError. This race was quite rare---we've seen it only a handful of times on the buildbots, and I've only managed to trigger it once locally---but the issue and fix have been verified by TSan. Big thanks to @gottesmm for getting a TSan build up and running so we could use it here.
Resolved bug number: (rdar://problem/27541751)
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