Improve example in 15.2 Work queues with error handling and cleanup #317
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Previously, sched_init() did not check whether alloc_workqueue() succeeded. This could lead to a NULL pointer dereference and kernel crash if memory allocation failed. This commit adds a check for a NULL return and logs an error message if allocation fails. By returning -ENOMEM early, we ensure the module will not be loaded in an invalid state and avoid undefined behavior or system instability.
jserv
reviewed
May 5, 2025
To ensure no work is left running when the module is removed, call
flush_workqueue() before destroy_workqueue() in the module exit path.
According to the kernel documentation, destroy_workqueue() expects
that all work items have already completed:
"Safely destroy a workqueue. All work currently pending will be
done first."
This change adds an explicit call to flush_workqueue() in the module
exit function to ensure no work handler remains in progress or pending
at the time of destruction.
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Okay, here's the updated version |
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Thank @wurrrrrrrrrr for contributing! |
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Since the example in Chapter 15.2 demonstrates the use of work queues in kernel modules, improving its reliability with proper error handling and cleanup logic helps reflect best practices in modern kernel development. This change enhances safety by preventing null pointer dereference during allocation failure and ensuring all work is completed before module unload.
Summary by Bito
This pull request improves the example in Chapter 15.2, "Work queues", by adding error handling for alloc_workqueue() and ensuring flush_workqueue() is called before destroy_workqueue() in the module exit path. These changes align the code with kernel best practices, prevent common pitfalls like null pointer dereference, and make the example safer for readers and learners on modern kernels.
These changes improve robustness in the workqueue lifecycle and reduce the risk of memory corruption.
Unit_tests added : False
** Estimated effort to review (1-5, lower is better)** : 2