[PATCH v2 0/3] rcu/nocb: Few NOCB cleanup patches

[Joel Fernandes <joelagnelf@nvidia.com>]

This series removes an unnecessary wake path (WakeOvfIsDeferred) from
the NOCB code and adds debugging warnings to detect any potential lost
wakeups.

The WakeOvfIsDeferred code path in __call_rcu_nocb_wake() attempts to
wake rcuog when the callback count exceeds qhimark and callbacks aren't
done with their GP. However, testing proves this wake is always
redundant or useless - in the flooding case, rcuog is always waiting
for a GP to finish, so waking it up is pointless.

All NOCB rcutorture scenarios pass (TREE01, TREE05, TREE08).

Changes since v1:
- Split into separate patches as suggested by Frederic
- Removed the pairing smp_mb__after_spin_lock() in
  do_nocb_deferred_wakeup_timer() as noted by Frederic.

Link to v1 (RFC):
https://lore.kernel.org/all/20251225074451.2405584-1-joelagnelf@nvidia.com/

Joel Fernandes (3):
  rcu/nocb: Remove unnecessary WakeOvfIsDeferred wake path
  rcu/nocb: Add warning if no rcuog wake up attempt happened during
    overload
  rcu/nocb: Add warning to detect if overload advancement is ever useful

 kernel/rcu/tree.c      |  2 ++
 kernel/rcu/tree.h      |  2 +-
 kernel/rcu/tree_nocb.h | 53 +++++++++++++++++++++---------------------
 3 files changed, 29 insertions(+), 28 deletions(-)

--
2.34.1