1 files changed, 32 insertions, 54 deletions

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 32798eb14853..1a1c1047d2ed 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -38,8 +38,8 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 	sp->srcu_lock_nesting[0] = 0;
 	sp->srcu_lock_nesting[1] = 0;
 	init_swait_queue_head(&sp->srcu_wq);
-	sp->srcu_gp_seq = 0;
-	rcu_segcblist_init(&sp->srcu_cblist);
+	sp->srcu_cb_head = NULL;
+	sp->srcu_cb_tail = &sp->srcu_cb_head;
 	sp->srcu_gp_running = false;
 	sp->srcu_gp_waiting = false;
 	sp->srcu_idx = 0;
@@ -88,30 +88,14 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 {
 	WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
 	flush_work(&sp->srcu_work);
-	WARN_ON(rcu_seq_state(sp->srcu_gp_seq));
 	WARN_ON(sp->srcu_gp_running);
 	WARN_ON(sp->srcu_gp_waiting);
-	WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist));
+	WARN_ON(sp->srcu_cb_head);
+	WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
 }
 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
 /*
- * Counts the new reader in the appropriate per-CPU element of the
- * srcu_struct.  Can be invoked from irq/bh handlers, but the matching
- * __srcu_read_unlock() must be in the same handler instance.  Returns an
- * index that must be passed to the matching srcu_read_unlock().
- */
-int __srcu_read_lock(struct srcu_struct *sp)
-{
-	int idx;
-
-	idx = READ_ONCE(sp->srcu_idx);
-	WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
-	return idx;
-}
-EXPORT_SYMBOL_GPL(__srcu_read_lock);
-
-/*
  * Removes the count for the old reader from the appropriate element of
  * the srcu_struct.
  */
@@ -133,52 +117,44 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 void srcu_drive_gp(struct work_struct *wp)
 {
 	int idx;
-	struct rcu_cblist ready_cbs;
-	struct srcu_struct *sp;
+	struct rcu_head *lh;
 	struct rcu_head *rhp;
+	struct srcu_struct *sp;
 
 	sp = container_of(wp, struct srcu_struct, srcu_work);
-	if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist))
+	if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head))
 		return; /* Already running or nothing to do. */
 
-	/* Tag recently arrived callbacks and wait for readers. */
+	/* Remove recently arrived callbacks and wait for readers. */
 	WRITE_ONCE(sp->srcu_gp_running, true);
-	rcu_segcblist_accelerate(&sp->srcu_cblist,
-				 rcu_seq_snap(&sp->srcu_gp_seq));
-	rcu_seq_start(&sp->srcu_gp_seq);
+	local_irq_disable();
+	lh = sp->srcu_cb_head;
+	sp->srcu_cb_head = NULL;
+	sp->srcu_cb_tail = &sp->srcu_cb_head;
+	local_irq_enable();
 	idx = sp->srcu_idx;
 	WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
 	WRITE_ONCE(sp->srcu_gp_waiting, true);  /* srcu_read_unlock() wakes! */
 	swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
 	WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
-	rcu_seq_end(&sp->srcu_gp_seq);
-
-	/* Update callback list based on GP, and invoke ready callbacks. */
-	rcu_segcblist_advance(&sp->srcu_cblist,
-			      rcu_seq_current(&sp->srcu_gp_seq));
-	if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) {
-		rcu_cblist_init(&ready_cbs);
-		local_irq_disable();
-		rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs);
-		local_irq_enable();
-		rhp = rcu_cblist_dequeue(&ready_cbs);
-		for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
-			local_bh_disable();
-			rhp->func(rhp);
-			local_bh_enable();
-		}
-		local_irq_disable();
-		rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs);
-		local_irq_enable();
+
+	/* Invoke the callbacks we removed above. */
+	while (lh) {
+		rhp = lh;
+		lh = lh->next;
+		local_bh_disable();
+		rhp->func(rhp);
+		local_bh_enable();
 	}
-	WRITE_ONCE(sp->srcu_gp_running, false);
 
 	/*
-	 * If more callbacks, reschedule ourselves.  This can race with
-	 * a call_srcu() at interrupt level, but the ->srcu_gp_running
-	 * checks will straighten that out.
+	 * Enable rescheduling, and if there are more callbacks,
+	 * reschedule ourselves.  This can race with a call_srcu()
+	 * at interrupt level, but the ->srcu_gp_running checks will
+	 * straighten that out.
 	 */
-	if (!rcu_segcblist_empty(&sp->srcu_cblist))
+	WRITE_ONCE(sp->srcu_gp_running, false);
+	if (READ_ONCE(sp->srcu_cb_head))
 		schedule_work(&sp->srcu_work);
 }
 EXPORT_SYMBOL_GPL(srcu_drive_gp);
@@ -187,14 +163,16 @@ EXPORT_SYMBOL_GPL(srcu_drive_gp);
  * Enqueue an SRCU callback on the specified srcu_struct structure,
  * initiating grace-period processing if it is not already running.
  */
-void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
+void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
 	       rcu_callback_t func)
 {
 	unsigned long flags;
 
-	head->func = func;
+	rhp->func = func;
+	rhp->next = NULL;
 	local_irq_save(flags);
-	rcu_segcblist_enqueue(&sp->srcu_cblist, head, false);
+	*sp->srcu_cb_tail = rhp;
+	sp->srcu_cb_tail = &rhp->next;
 	local_irq_restore(flags);
 	if (!READ_ONCE(sp->srcu_gp_running))
 		schedule_work(&sp->srcu_work);