[Concurrency] Fix alreadyLocked in withStatusRecordLock. #81205
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If the preloaded status is locked, then we need to reload it in order to distinguish between the current thread holding the lock and another thread holding the lock. Without this, if another thread holds the lock, then we won't set the is-locked bit. We'll still actually hold the lock, but other threads may perform operations locklessly if the bit is not set, which can cause a crash. By reloading status in that case, we ensure that the bit is always set correctly. This manifested as crashes in task cancellation but could cause other task-related issues as well. Also remove an assert of !isStatusRecordLocked() in AsyncTask::complete(). We allow other threads to access tasks and take the lock for things like cancellation, so the lock may legitimately be held at that point. rdar://150327908
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@swift-ci please test |
ktoso
reviewed
Apr 30, 2025
| assert(!oldStatus.isStatusRecordLocked() && | ||
| "Task is completing, cannot be locked anymore!"); | ||
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| // Don't assert !isStatusRecordLocked(). It can be legitimately true here, |
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Can be legitimately false rather, right.
ktoso
approved these changes
Apr 30, 2025
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If the preloaded status is locked, then we need to reload it in order to distinguish between the current thread holding the lock and another thread holding the lock. Without this, if another thread holds the lock, then we won't set the is-locked bit. We'll still actually hold the lock, but other threads may perform operations locklessly if the bit is not set, which can cause a crash. By reloading status in that case, we ensure that the bit is always set correctly.
This manifested as crashes in task cancellation but could cause other task-related issues as well.
Also remove an assert of !isStatusRecordLocked() in AsyncTask::complete(). We allow other threads to access tasks and take the lock for things like cancellation, so the lock may legitimately be held at that point.
rdar://150327908