v4.19.13 snapshot.
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
new file mode 100644
index 0000000..04fc2ed
--- /dev/null
+++ b/kernel/rcu/srcutiny.c
@@ -0,0 +1,206 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ * tiny version for non-preemptible single-CPU use.
+ *
+ * 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>
+ */
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+
+#include <linux/rcu_node_tree.h>
+#include "rcu_segcblist.h"
+#include "rcu.h"
+
+int rcu_scheduler_active __read_mostly;
+
+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_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;
+ INIT_WORK(&sp->srcu_work, srcu_drive_gp);
+ return 0;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+ struct lock_class_key *key)
+{
+ /* Don't re-initialize a lock while it is held. */
+ debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+ lockdep_init_map(&sp->dep_map, name, key, 0);
+ return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function. Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+ return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
+{
+ WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
+ if (quiesced)
+ WARN_ON(work_pending(&sp->srcu_work));
+ else
+ flush_work(&sp->srcu_work);
+ WARN_ON(sp->srcu_gp_running);
+ WARN_ON(sp->srcu_gp_waiting);
+ WARN_ON(sp->srcu_cb_head);
+ WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
+}
+EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
+
+/*
+ * Removes the count for the old reader from the appropriate element of
+ * the srcu_struct.
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+ int newval = sp->srcu_lock_nesting[idx] - 1;
+
+ WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
+ if (!newval && READ_ONCE(sp->srcu_gp_waiting))
+ swake_up_one(&sp->srcu_wq);
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * Workqueue handler to drive one grace period and invoke any callbacks
+ * that become ready as a result. Single-CPU and !PREEMPT operation
+ * means that we get away with murder on synchronization. ;-)
+ */
+void srcu_drive_gp(struct work_struct *wp)
+{
+ int idx;
+ 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 || !READ_ONCE(sp->srcu_cb_head))
+ return; /* Already running or nothing to do. */
+
+ /* Remove recently arrived callbacks and wait for readers. */
+ WRITE_ONCE(sp->srcu_gp_running, true);
+ 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_exclusive(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
+ WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
+
+ /* Invoke the callbacks we removed above. */
+ while (lh) {
+ rhp = lh;
+ lh = lh->next;
+ local_bh_disable();
+ rhp->func(rhp);
+ local_bh_enable();
+ }
+
+ /*
+ * 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.
+ */
+ 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);
+
+/*
+ * 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 *rhp,
+ rcu_callback_t func)
+{
+ unsigned long flags;
+
+ rhp->func = func;
+ rhp->next = NULL;
+ local_irq_save(flags);
+ *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);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+/*
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+ struct rcu_synchronize rs;
+
+ init_rcu_head_on_stack(&rs.head);
+ init_completion(&rs.completion);
+ call_srcu(sp, &rs.head, wakeme_after_rcu);
+ wait_for_completion(&rs.completion);
+ destroy_rcu_head_on_stack(&rs.head);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/* Lockdep diagnostics. */
+void __init rcu_scheduler_starting(void)
+{
+ rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+}