1 files changed, 284 insertions, 0 deletions
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
new file mode 100644
index 0000000000..336af24e0f
--- /dev/null
+++ b/kernel/rcu/srcutiny.c
@@ -0,0 +1,284 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion,
+ *	tiny version for non-preemptible single-CPU use.
+ *
+ * Copyright (C) IBM Corporation, 2017
+ *
+ * Author: Paul McKenney <paulmck@linux.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 LIST_HEAD(srcu_boot_list);
+static bool srcu_init_done;
+
+static int init_srcu_struct_fields(struct srcu_struct *ssp)
+{
+	ssp->srcu_lock_nesting[0] = 0;
+	ssp->srcu_lock_nesting[1] = 0;
+	init_swait_queue_head(&ssp->srcu_wq);
+	ssp->srcu_cb_head = NULL;
+	ssp->srcu_cb_tail = &ssp->srcu_cb_head;
+	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;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
+		       struct lock_class_key *key)
+{
+	/* Don't re-initialize a lock while it is held. */
+	debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
+	lockdep_init_map(&ssp->dep_map, name, key, 0);
+	return init_srcu_struct_fields(ssp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @ssp: 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 *ssp)
+{
+	return init_srcu_struct_fields(ssp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @ssp: 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 *ssp)
+{
+	WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
+	flush_work(&ssp->srcu_work);
+	WARN_ON(ssp->srcu_gp_running);
+	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);
+
+/*
+ * Removes the count for the old reader from the appropriate element of
+ * the srcu_struct.
+ */
+void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
+{
+	int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
+
+	WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
+	if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task())
+		swake_up_one(&ssp->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 !PREEMPTION 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 *ssp;
+
+	ssp = container_of(wp, struct srcu_struct, srcu_work);
+	if (ssp->srcu_gp_running || ULONG_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. */
+	WRITE_ONCE(ssp->srcu_gp_running, true);
+	local_irq_disable();
+	lh = ssp->srcu_cb_head;
+	ssp->srcu_cb_head = NULL;
+	ssp->srcu_cb_tail = &ssp->srcu_cb_head;
+	local_irq_enable();
+	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) {
+		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(ssp->srcu_gp_running, false);
+	if (ULONG_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 long cookie;
+
+	cookie = get_state_synchronize_srcu(ssp);
+	if (ULONG_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.
+ */
+void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
+	       rcu_callback_t func)
+{
+	unsigned long flags;
+
+	rhp->func = func;
+	rhp->next = NULL;
+	local_irq_save(flags);
+	*ssp->srcu_cb_tail = rhp;
+	ssp->srcu_cb_tail = &rhp->next;
+	local_irq_restore(flags);
+	srcu_gp_start_if_needed(ssp);
+}
+EXPORT_SYMBOL_GPL(call_srcu);
+
+/*
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ */
+void synchronize_srcu(struct srcu_struct *ssp)
+{
+	struct rcu_synchronize rs;
+
+	srcu_lock_sync(&ssp->dep_map);
+
+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
+			lock_is_held(&rcu_bh_lock_map) ||
+			lock_is_held(&rcu_lock_map) ||
+			lock_is_held(&rcu_sched_lock_map),
+			"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
+
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
+
+	might_sleep();
+	init_rcu_head_on_stack(&rs.head);
+	init_completion(&rs.completion);
+	call_srcu(ssp, &rs.head, wakeme_after_rcu);
+	wait_for_completion(&rs.completion);
+	destroy_rcu_head_on_stack(&rs.head);
+}
+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;
+}
+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)
+{
+	unsigned long cur_s = READ_ONCE(ssp->srcu_idx);
+
+	barrier();
+	return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
+
+/* Lockdep diagnostics.  */
+void __init rcu_scheduler_starting(void)
+{
+	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+}
+
+/*
+ * Queue work for srcu_struct structures with early boot callbacks.
+ * The work won't actually execute until the workqueue initialization
+ * phase that takes place after the scheduler starts.
+ */
+void __init srcu_init(void)
+{
+	struct srcu_struct *ssp;
+
+	srcu_init_done = true;
+	while (!list_empty(&srcu_boot_list)) {
+		ssp = list_first_entry(&srcu_boot_list,
+				      struct srcu_struct, srcu_work.entry);
+		list_del_init(&ssp->srcu_work.entry);
+		schedule_work(&ssp->srcu_work);
+	}
+}