rcu: Add full-sized polling for get_state()

The get_state_synchronize_rcu() API compresses the combined expedited and
normal grace-period states into a single unsigned long, which conserves
storage, but can miss grace periods in certain cases involving overlapping
normal and expedited grace periods.  Missing the occasional grace period
is usually not a problem, but there are use cases that care about each
and every grace period.

This commit therefore adds the next member of the full-state RCU
grace-period polling API, namely the get_state_synchronize_rcu_full()
function.  This uses up to three times the storage (rcu_gp_oldstate
structure instead of unsigned long), but is guaranteed not to miss
grace periods.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 4ccbc3aa9dc2..7b769f1b417a 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -50,6 +50,7 @@ struct rcu_gp_oldstate {
 unsigned long start_poll_synchronize_rcu_expedited(void);
 void cond_synchronize_rcu_expedited(unsigned long oldstate);
 unsigned long get_state_synchronize_rcu(void);
+void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
 unsigned long start_poll_synchronize_rcu(void);
 bool poll_state_synchronize_rcu(unsigned long oldstate);
 bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);