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[[meta title="Fix libdiskfs Locking Issues"]]

Nowadays the most often encountered cause of Hurd crashes seems to be lockups
in the [[hurd/translator/ext2fs]] server.  One of these could be traced
recently, and turned out to be a lock inside [[hurd/libdiskfs]] that was taken
and not released in some cases.  There is reason to believe that there are more
faulty paths causing these lockups.

The task is systematically checking the [[hurd/libdiskfs]] code for this kind of locking
issues. To achieve this, some kind of test harness has to be implemented: For
exmple instrumenting the code to check locking correctness constantly at
runtime. Or implementing a unit testing framework that explicitely checks
locking in various code paths. (The latter could serve as a template for
implementing unit checks in other parts of the Hurd codebase...)

This task requires experience with debugging locking issues in multithreaded
applications.

Possible mentors: ?

Exercise: Hack libdiskfs to keep count of the number of locks currently held.