Add a Rust abstraction for sleepable RCU (SRCU), backed by C srcu_struct.
Provide FFI helpers and a safe wrapper with a guard-based API for read-side
critical sections.
Cleanup is handled via `PinnedDrop`. It first checks for active read-side
sections and emits a warning if any guards were leaked. In that case, it
waits in `synchronize_srcu()` rather than risking a UAF by freeing the
`srcu_struct` that is still reachable from the C side. It then uses
`srcu_barrier()` to drain pending callbacks before finally calling
`cleanup_srcu_struct()`.
Signed-off-by: Onur Özkan <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
