Fix null dereference in logging in Task #119563
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If Task.Start and Task.Wait are used concurrently, it's possible for Wait to execute the task as part of the inlining logic, causing the task's completion logic to null out its m_action during the call to Start. This isn't generally a functional issue, as synchronization ensures it's only ever invoked once, however EventSource-based tracing code may try to extract the method name from the delegate, and it can end up hitting an ArgumentNullException due to the race causing the delegate to be null.
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Pull Request Overview
This PR fixes a null dereference exception in Task logging that occurs when Task.Start and Task.Wait are called concurrently. The race condition can cause the task's m_action field to be nulled out during execution, leading to an ArgumentNullException when EventSource-based tracing attempts to extract the method name from a null delegate.
Key changes:
- Added null check for m_action before using it in logging
- Introduced pattern matching to safely capture the delegate reference
- Removed defensive Debug.Assert that was no longer applicable
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Tagging subscribers to this area: @dotnet/area-system-threading-tasks |
MihaZupan
approved these changes
Sep 12, 2025
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If Task.Start and Task.Wait are used concurrently, it's possible for Wait to execute the task as part of the inlining logic, causing the task's completion logic to null out its m_action during the call to Start. This isn't generally a functional issue, as synchronization ensures it's only ever invoked once, however EventSource-based tracing code may try to extract the method name from the delegate, and it can end up hitting an ArgumentNullException due to the race causing the delegate to be null.
Fixes #119484