Review srcu grace period sequence number assignments

[KunWuChan]

Add instrumentation for SRCU grace period sequence number fields to verify their correct behavior and placement.

The fields srcu_gp_seq_needed and srcu_gp_seq_needed_exp in srcu_data, srcu_node, and srcu_usage structures track grace period sequence numbers. This PR provides tools (bpftrace scripts, tracepoints patch, GDB guide) to dynamically observe and confirm that their assignments are correctly layered, synchronized, and serve their distinct purposes (local wrap, tree funneling, global scheduling) without consolidation issues.

---

 

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
_{Learn more about Cursor Agents}