may need the clock lock for nanotime().
- Add KTR trace events for lock list manipulations and other witness
operations.
- Use a temporary variable instead of setting the lock list head directly
and then setting up the links to add a new lock list entry to the lock
list. This small race could result in witness "forgetting" about all
the locks held by this process temporarily during an interrupt.
- Close a more fatal race condition when removing a lock from a list.
Removing a lock from the list entails both decrementing the count of
items in this bucket as well as shuffling items in the current bucket up
a notch to replace the gap left by the removed item. Wrap these
operations in a critical section.
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