srcu: Fill out polled grace-period APIs

This commit adds the get_completed_synchronize_srcu() and the
same_state_synchronize_srcu() functions.  The first returns a cookie
that is always interpreted as corresponding to an expired grace period.
The second does an equality comparison of a pair of cookies.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index f664cba7a80c..6f6cb5fc1242 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -57,6 +57,20 @@ void cleanup_srcu_struct(struct srcu_struct *ssp);
 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
 void synchronize_srcu(struct srcu_struct *ssp);
+
+#define SRCU_GET_STATE_COMPLETED 0x1
+
+/**
+ * get_completed_synchronize_srcu - Return a pre-completed polled state cookie
+ *
+ * Returns a value that poll_state_synchronize_srcu() will always treat
+ * as a cookie whose grace period has already completed.
+ */
+static inline unsigned long get_completed_synchronize_srcu(void)
+{
+	return SRCU_GET_STATE_COMPLETED;
+}
+
 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
@@ -65,6 +79,23 @@ bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
 // not-yet-completed SRCU grace periods.
 #define NUM_ACTIVE_SRCU_POLL_OLDSTATE 2
 
+/**
+ * same_state_synchronize_srcu - Are two old-state values identical?
+ * @oldstate1: First old-state value.
+ * @oldstate2: Second old-state value.
+ *
+ * The two old-state values must have been obtained from either
+ * get_state_synchronize_srcu(), start_poll_synchronize_srcu(), or
+ * get_completed_synchronize_srcu().  Returns @true if the two values are
+ * identical and @false otherwise.  This allows structures whose lifetimes
+ * are tracked by old-state values to push these values to a list header,
+ * allowing those structures to be slightly smaller.
+ */
+static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned long oldstate2)
+{
+	return oldstate1 == oldstate2;
+}
+
 #ifdef CONFIG_NEED_SRCU_NMI_SAFE
 int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
 void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);