rcu: Update comments for gp_seq and expedited GP tracking

Update documentation comments throughout the RCU callback infrastructure
to reflect the transition from a single grace-period sequence number to
the full struct rcu_gp_seq that tracks both normal and expedited grace
periods.

The ->gp_seq[] array documentation in rcu_segcblist.h is updated to
describe dual (normal and expedited) GP tracking.  The
rcu_segcblist_advance(), rcu_segcblist_accelerate(), and
rcu_advance_cbs() comments are updated to refer to the struct rcu_gp_seq
state (gsp) instead of the old bare grace-period sequence number (seq).

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index 137cc23b024c..08b63ecf719b 100644
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -50,12 +50,14 @@ struct rcu_cblist {
  * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
  * empty.
  *
- * The ->gp_seq[] array contains the grace-period number at which the
- * corresponding segment of callbacks will be ready to invoke.  A given
- * element of this array is meaningful only when the corresponding segment
- * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
- * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
- * not yet been assigned a grace-period number).
+ * The ->gp_seq[] array contains the grace-period state at which the
+ * corresponding segment of callbacks will be ready to invoke.  This tracks
+ * both normal and expedited grace periods, allowing callbacks to complete
+ * when either type of GP finishes.  A given element of this array is
+ * meaningful only when the corresponding segment is non-empty, and it is
+ * never valid for RCU_DONE_TAIL (whose callbacks are already ready to
+ * invoke) or for RCU_NEXT_TAIL (whose callbacks have not yet been assigned
+ * a grace-period state).
  */
 #define RCU_DONE_TAIL		0	/* Also RCU_WAIT head. */
 #define RCU_WAIT_TAIL		1	/* Also RCU_NEXT_READY head. */