March 2026 Monthly Summary – nxp-upstream/zephyr Key features delivered: - Inter-Processor Interrupt (IPI) race condition fix in kernel/sched. Implemented by moving signal_pending_ipi() inside the K_SPINLOCK block in z_get_next_switch_handle(), ensuring atomic IPI dispatch and preventing hangs in multi-core configurations. Commit: 1666066082a8e917e8a0beb58f596634797e48df. - Additional hardening in reschedule paths: fixed race patterns in reschedule() and added TODO note for z_reschedule_irqlock() (it currently does not take the sched spinlock). Major bugs fixed: - Resolved a potential permanent hang caused by a race in handling self-directed IPIs, which could occur when a CPU could wake from WFI but never receive a correctly scheduled IPI due to a timing window between lock release and IPI dispatch. Overall impact and accomplishments: - Significantly improved reliability and determinism of multi-core scheduling, reducing hang risk in virtualized and descheduled environments. - Improved wakeup latency consistency and reduced unnecessary rescheduling latency related to IPI handling, contributing to tighter performance envelopes for multi-threaded workloads. Technologies/skills demonstrated: - Kernel synchronization and scheduling (spinlocks, IPIs, sched locks) - Debugging and fixing race conditions in low-level kernel code - Code review and commit-driven development in a critical subsystem (C language) - Emphasis on business value: increased stability for multi-core deployments and virtualization scenarios.