1 files changed, 67 insertions, 10 deletions

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 6208c1dae5c9..26344dc6483b 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -34,6 +34,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp)
 	ssp->srcu_gp_running = false;
 	ssp->srcu_gp_waiting = false;
 	ssp->srcu_idx = 0;
+	ssp->srcu_idx_max = 0;
 	INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
 	INIT_LIST_HEAD(&ssp->srcu_work.entry);
 	return 0;
@@ -84,6 +85,8 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
 	WARN_ON(ssp->srcu_gp_waiting);
 	WARN_ON(ssp->srcu_cb_head);
 	WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
+	WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max);
+	WARN_ON(ssp->srcu_idx & 0x1);
 }
 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
@@ -114,7 +117,7 @@ void srcu_drive_gp(struct work_struct *wp)
 	struct srcu_struct *ssp;
 
 	ssp = container_of(wp, struct srcu_struct, srcu_work);
-	if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
+	if (ssp->srcu_gp_running || USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
 		return; /* Already running or nothing to do. */
 
 	/* Remove recently arrived callbacks and wait for readers. */
@@ -124,11 +127,12 @@ void srcu_drive_gp(struct work_struct *wp)
 	ssp->srcu_cb_head = NULL;
 	ssp->srcu_cb_tail = &ssp->srcu_cb_head;
 	local_irq_enable();
-	idx = ssp->srcu_idx;
-	WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
+	idx = (ssp->srcu_idx & 0x2) / 2;
+	WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
 	WRITE_ONCE(ssp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 	swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
 	WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
+	WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
 
 	/* Invoke the callbacks we removed above. */
 	while (lh) {
@@ -146,11 +150,27 @@ void srcu_drive_gp(struct work_struct *wp)
 	 * straighten that out.
 	 */
 	WRITE_ONCE(ssp->srcu_gp_running, false);
-	if (READ_ONCE(ssp->srcu_cb_head))
+	if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
 		schedule_work(&ssp->srcu_work);
 }
 EXPORT_SYMBOL_GPL(srcu_drive_gp);
 
+static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
+{
+	unsigned short cookie;
+
+	cookie = get_state_synchronize_srcu(ssp);
+	if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
+		return;
+	WRITE_ONCE(ssp->srcu_idx_max, cookie);
+	if (!READ_ONCE(ssp->srcu_gp_running)) {
+		if (likely(srcu_init_done))
+			schedule_work(&ssp->srcu_work);
+		else if (list_empty(&ssp->srcu_work.entry))
+			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
+	}
+}
+
 /*
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
@@ -166,12 +186,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	*ssp->srcu_cb_tail = rhp;
 	ssp->srcu_cb_tail = &rhp->next;
 	local_irq_restore(flags);
-	if (!READ_ONCE(ssp->srcu_gp_running)) {
-		if (likely(srcu_init_done))
-			schedule_work(&ssp->srcu_work);
-		else if (list_empty(&ssp->srcu_work.entry))
-			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
-	}
+	srcu_gp_start_if_needed(ssp);
 }
 EXPORT_SYMBOL_GPL(call_srcu);
 
@@ -190,6 +205,48 @@ void synchronize_srcu(struct srcu_struct *ssp)
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
+/*
+ * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
+ */
+unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
+{
+	unsigned long ret;
+
+	barrier();
+	ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
+	barrier();
+	return ret & USHRT_MAX;
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
+
+/*
+ * start_poll_synchronize_srcu - Provide cookie and start grace period
+ *
+ * The difference between this and get_state_synchronize_srcu() is that
+ * this function ensures that the poll_state_synchronize_srcu() will
+ * eventually return the value true.
+ */
+unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
+{
+	unsigned long ret = get_state_synchronize_srcu(ssp);
+
+	srcu_gp_start_if_needed(ssp);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
+
+/*
+ * poll_state_synchronize_srcu - Has cookie's grace period ended?
+ */
+bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
+{
+	bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie);
+
+	barrier();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
 /* Lockdep diagnostics.  */
 void __init rcu_scheduler_starting(void)
 {