srcu: Create a tiny SRCU

In response to automated complaints about modifications to SRCU
increasing its size, this commit creates a tiny SRCU that is
used in SMP=n && PREEMPT=n builds.

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

1 files changed, 81 insertions, 0 deletions

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
new file mode 100644
index 000000000000..4f284e4f4d8c
--- /dev/null
+++ b/include/linux/srcutiny.h
@@ -0,0 +1,81 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tiny variant.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ */
+
+#ifndef _LINUX_SRCU_TINY_H
+#define _LINUX_SRCU_TINY_H
+
+#include <linux/swait.h>
+
+struct srcu_struct {
+	int srcu_lock_nesting[2];	/* srcu_read_lock() nesting depth. */
+	struct swait_queue_head srcu_wq;
+					/* Last srcu_read_unlock() wakes GP. */
+	unsigned long srcu_gp_seq;	/* GP seq # for callback tagging. */
+	struct rcu_segcblist srcu_cblist;
+					/* Pending SRCU callbacks. */
+	int srcu_idx;			/* Current reader array element. */
+	bool srcu_gp_running;		/* GP workqueue running? */
+	bool srcu_gp_waiting;		/* GP waiting for readers? */
+	struct work_struct srcu_work;	/* For driving grace periods. */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+};
+
+void srcu_drive_gp(struct work_struct *wp);
+
+#define __SRCU_STRUCT_INIT(name)					\
+{									\
+	.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),	\
+	.srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),	\
+	.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp),	\
+	__SRCU_DEP_MAP_INIT(name)					\
+}
+
+/*
+ * This odd _STATIC_ arrangement is needed for API compatibility with
+ * Tree SRCU, which needs some per-CPU data.
+ */
+#define DEFINE_SRCU(name) \
+	struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+#define DEFINE_STATIC_SRCU(name) \
+	static struct srcu_struct name = __SRCU_STRUCT_INIT(name)
+
+void synchronize_srcu(struct srcu_struct *sp);
+
+static inline void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+
+static inline void srcu_barrier(struct srcu_struct *sp)
+{
+	synchronize_srcu(sp);
+}
+
+static inline unsigned long srcu_batches_completed(struct srcu_struct *sp)
+{
+	return 0;
+}
+
+#endif