/* Advance CBs to reduce false positives below. */
offloaded = rcu_rdp_is_offloaded(rdp);
if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
+
+ // We get here if a grace period was needed (“needgp”)
+ // and the above call to rcu_accelerate_cbs() did not set
+ // the RCU_GP_FLAG_INIT bit in ->gp_state (which records
+ // the need for another grace period). The purpose
+ // of the “offloaded” check is to avoid invoking
+ // rcu_accelerate_cbs() on an offloaded CPU because we do not
+ // hold the ->nocb_lock needed to safely access an offloaded
+ // ->cblist. We do not want to acquire that lock because
+ // it can be heavily contended during callback floods.
+
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
- trace_rcu_grace_period(rcu_state.name,
- rcu_state.gp_seq,
- TPS("newreq"));
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
} else {
- WRITE_ONCE(rcu_state.gp_flags,
- rcu_state.gp_flags & RCU_GP_FLAG_INIT);
+
+ // We get here either if there is no need for an
+ // additional grace period or if rcu_accelerate_cbs() has
+ // already set the RCU_GP_FLAG_INIT bit in ->gp_flags.
+ // So all we need to do is to clear all of the other
+ // ->gp_flags bits.
+
+ WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
}
raw_spin_unlock_irq_rcu_node(rnp);