Reference counters are widely used inside the kernel to avoid race conditions due to the concurrent allocation and releasing of a resource. A reference counter is just an atomic_t counter associated with a specific resource like a memory page, a module, or a file. The counter is atomically incremented when a kernel control path starts using the resource, and it is decremented when a kernel control path finishes using the resource. When the reference counter becomes zero, the resource is not being used, and it can be released if necessary.
Continue reading here: The Global Kernel Lock
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