RCU stands for Read-Copy-Update, a Linux synchronization pattern built for fast reads in shared kernel data structures. Readers can access data without taking a heavy lock, while updaters make a copy, change it, and then retire the old version after a grace period. That delay helps ensure that any CPU still using the old object can finish safely.
RCU matters in security because many kernel subsystems use it to manage object lifetime under concurrency. If teardown happens too early, stale pointers can become use-after-free bugs, which attackers may try to turn into crashes or privilege escalation. In practice, bugs involving network or scheduler code often hinge on whether an object was removed, freed, or still reachable by another thread. Defenders look for proper RCU grace periods, correct reference counting, and testing tools such as KASAN to catch lifetime mistakes before release.