Bug in flock(3) in 4.2BSD.

[Stephen J. Muir]

Consider the following scenario:
1. process 0 starts and opens a file
2. process 1 starts and opens the same file
3. process 2 starts and opens the same file
4. process 1 applies a shared lock and succeeds
5. process 2 attempts to apply an exclusive lock and hangs
6. process 1 attempts to upgrade its lock to an exclusive one and hangs

Process 1 should not have hung here.

7. I kill process 2

Process 1 is still hung.

8. I kill process 1
9. process 3 starts and opens the same file
10. process 3 attempts to apply an exclusive lock and hangs

Process 3 should not have hung here.

11. I kill processes 0 & 3
12. process 4 starts and opens the same file
13. process 4 applies an exclusive lock and succeeds

This is correct.
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