srcu: Crude control of expedited grace periods

SRCU's implementation of expedited grace periods has always assumed
that the SRCU instance is idle when the expedited request arrives.
This commit improves this a bit by maintaining a count of the number
of outstanding expedited requests, thus allowing prior non-expedited
grace periods accommodate these requests by shifting to expedited mode.
However, any non-expedited wait already in progress will still wait for
the full duration.

Improved control of expedited grace periods is planned, but one step
at a time.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index e7dbc01b61a1..73a1b6296224 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -42,6 +42,7 @@ struct srcu_array {
 struct srcu_struct {
         unsigned long completed;
         unsigned long srcu_gp_seq;
+        atomic_t srcu_exp_cnt;
         struct srcu_array __percpu *per_cpu_ref;
         spinlock_t queue_lock; /* protect ->srcu_cblist */
         struct rcu_segcblist srcu_cblist;