v4.19.13 snapshot.
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
new file mode 100644
index 0000000..f41d2fb
--- /dev/null
+++ b/include/linux/srcutiny.h
@@ -0,0 +1,103 @@
+/*
+ * 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 {
+ short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
+ short srcu_idx; /* Current reader array element. */
+ u8 srcu_gp_running; /* GP workqueue running? */
+ u8 srcu_gp_waiting; /* GP waiting for readers? */
+ struct swait_queue_head srcu_wq;
+ /* Last srcu_read_unlock() wakes GP. */
+ struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
+ struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
+ 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, __ignored) \
+{ \
+ .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
+ .srcu_cb_tail = &name.srcu_cb_head, \
+ .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, name)
+#define DEFINE_STATIC_SRCU(name) \
+ static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
+
+void synchronize_srcu(struct srcu_struct *sp);
+
+/*
+ * 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().
+ */
+static inline 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;
+}
+
+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);
+}
+
+/* Defined here to avoid size increase for non-torture kernels. */
+static inline void srcu_torture_stats_print(struct srcu_struct *sp,
+ char *tt, char *tf)
+{
+ int idx;
+
+ idx = READ_ONCE(sp->srcu_idx) & 0x1;
+ pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
+ tt, tf, idx,
+ READ_ONCE(sp->srcu_lock_nesting[!idx]),
+ READ_ONCE(sp->srcu_lock_nesting[idx]));
+}
+
+#endif