D.2.7.3 Announce a Quiescent State to RCU
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D.2.7.3 Announce a Quiescent State to RCU

The afore-mentioned rcu_process_callbacks() function has several duties:

1. Determining when to take measures to end an over-long grace period (via force_quiescent_state()).
2. Taking appropriate action when some other CPU detected the end of a grace period (via rcu_process_gp_end()). ``Appropriate action`` includes advancing this CPU's callbacks and recording the new grace period. This same function updates state in response to some other CPU starting a new grace period.
3. Reporting the current CPU's quiescent states to the core RCU mechanism (via rcu_check_quiescent_state(), which in turn invokes cpu_quiet()). This of course might mark the end of the current grace period.
4. Starting a new grace period if there is no grace period in progress and this CPU has RCU callbacks still waiting for a grace period (via cpu_needs_another_gp() and rcu_start_gp()).
5. Invoking any of this CPU's callbacks whose grace period has ended (via rcu_do_batch()).

These interactions are carefully orchestrated in order to avoid buggy behavior such as reporting a quiescent state from the previous grace period against the current grace period.