--- /dev/null
+/*
+ * RCU-based infrastructure for lightweight reader-writer locking
+ *
+ * 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) 2015, Red Hat, Inc.
+ *
+ * Author: Oleg Nesterov <oleg@redhat.com>
+ */
+
+#include <linux/rcu_sync.h>
+#include <linux/sched.h>
+
+#ifdef CONFIG_PROVE_RCU
+#define __INIT_HELD(func) .held = func,
+#else
+#define __INIT_HELD(func)
+#endif
+
+static const struct {
+ void (*sync)(void);
+ void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+ void (*wait)(void);
+#ifdef CONFIG_PROVE_RCU
+ int (*held)(void);
+#endif
+} gp_ops[] = {
+ [RCU_SYNC] = {
+ .sync = synchronize_rcu,
+ .call = call_rcu,
+ .wait = rcu_barrier,
+ __INIT_HELD(rcu_read_lock_held)
+ },
+ [RCU_SCHED_SYNC] = {
+ .sync = synchronize_sched,
+ .call = call_rcu_sched,
+ .wait = rcu_barrier_sched,
+ __INIT_HELD(rcu_read_lock_sched_held)
+ },
+ [RCU_BH_SYNC] = {
+ .sync = synchronize_rcu_bh,
+ .call = call_rcu_bh,
+ .wait = rcu_barrier_bh,
+ __INIT_HELD(rcu_read_lock_bh_held)
+ },
+};
+
+enum { GP_IDLE = 0, GP_PENDING, GP_PASSED };
+enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
+
+#define rss_lock gp_wait.lock
+
+#ifdef CONFIG_PROVE_RCU
+void rcu_sync_lockdep_assert(struct rcu_sync *rsp)
+{
+ RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(),
+ "suspicious rcu_sync_is_idle() usage");
+}
+#endif
+
+/**
+ * rcu_sync_init() - Initialize an rcu_sync structure
+ * @rsp: Pointer to rcu_sync structure to be initialized
+ * @type: Flavor of RCU with which to synchronize rcu_sync structure
+ */
+void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type)
+{
+ memset(rsp, 0, sizeof(*rsp));
+ init_waitqueue_head(&rsp->gp_wait);
+ rsp->gp_type = type;
+}
+
+/**
+ * rcu_sync_enter() - Force readers onto slowpath
+ * @rsp: Pointer to rcu_sync structure to use for synchronization
+ *
+ * This function is used by updaters who need readers to make use of
+ * a slowpath during the update. After this function returns, all
+ * subsequent calls to rcu_sync_is_idle() will return false, which
+ * tells readers to stay off their fastpaths. A later call to
+ * rcu_sync_exit() re-enables reader slowpaths.
+ *
+ * When called in isolation, rcu_sync_enter() must wait for a grace
+ * period, however, closely spaced calls to rcu_sync_enter() can
+ * optimize away the grace-period wait via a state machine implemented
+ * by rcu_sync_enter(), rcu_sync_exit(), and rcu_sync_func().
+ */
+void rcu_sync_enter(struct rcu_sync *rsp)
+{
+ bool need_wait, need_sync;
+
+ spin_lock_irq(&rsp->rss_lock);
+ need_wait = rsp->gp_count++;
+ need_sync = rsp->gp_state == GP_IDLE;
+ if (need_sync)
+ rsp->gp_state = GP_PENDING;
+ spin_unlock_irq(&rsp->rss_lock);
+
+ BUG_ON(need_wait && need_sync);
+
+ if (need_sync) {
+ gp_ops[rsp->gp_type].sync();
+ rsp->gp_state = GP_PASSED;
+ wake_up_all(&rsp->gp_wait);
+ } else if (need_wait) {
+ wait_event(rsp->gp_wait, rsp->gp_state == GP_PASSED);
+ } else {
+ /*
+ * Possible when there's a pending CB from a rcu_sync_exit().
+ * Nobody has yet been allowed the 'fast' path and thus we can
+ * avoid doing any sync(). The callback will get 'dropped'.
+ */
+ BUG_ON(rsp->gp_state != GP_PASSED);
+ }
+}
+
+/**
+ * rcu_sync_func() - Callback function managing reader access to fastpath
+ * @rsp: Pointer to rcu_sync structure to use for synchronization
+ *
+ * This function is passed to one of the call_rcu() functions by
+ * rcu_sync_exit(), so that it is invoked after a grace period following the
+ * that invocation of rcu_sync_exit(). It takes action based on events that
+ * have taken place in the meantime, so that closely spaced rcu_sync_enter()
+ * and rcu_sync_exit() pairs need not wait for a grace period.
+ *
+ * If another rcu_sync_enter() is invoked before the grace period
+ * ended, reset state to allow the next rcu_sync_exit() to let the
+ * readers back onto their fastpaths (after a grace period). If both
+ * another rcu_sync_enter() and its matching rcu_sync_exit() are invoked
+ * before the grace period ended, re-invoke call_rcu() on behalf of that
+ * rcu_sync_exit(). Otherwise, set all state back to idle so that readers
+ * can again use their fastpaths.
+ */
+static void rcu_sync_func(struct rcu_head *rcu)
+{
+ struct rcu_sync *rsp = container_of(rcu, struct rcu_sync, cb_head);
+ unsigned long flags;
+
+ BUG_ON(rsp->gp_state != GP_PASSED);
+ BUG_ON(rsp->cb_state == CB_IDLE);
+
+ spin_lock_irqsave(&rsp->rss_lock, flags);
+ if (rsp->gp_count) {
+ /*
+ * A new rcu_sync_begin() has happened; drop the callback.
+ */
+ rsp->cb_state = CB_IDLE;
+ } else if (rsp->cb_state == CB_REPLAY) {
+ /*
+ * A new rcu_sync_exit() has happened; requeue the callback
+ * to catch a later GP.
+ */
+ rsp->cb_state = CB_PENDING;
+ gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
+ } else {
+ /*
+ * We're at least a GP after rcu_sync_exit(); eveybody will now
+ * have observed the write side critical section. Let 'em rip!.
+ */
+ rsp->cb_state = CB_IDLE;
+ rsp->gp_state = GP_IDLE;
+ }
+ spin_unlock_irqrestore(&rsp->rss_lock, flags);
+}
+
+/**
+ * rcu_sync_exit() - Allow readers back onto fast patch after grace period
+ * @rsp: Pointer to rcu_sync structure to use for synchronization
+ *
+ * This function is used by updaters who have completed, and can therefore
+ * now allow readers to make use of their fastpaths after a grace period
+ * has elapsed. After this grace period has completed, all subsequent
+ * calls to rcu_sync_is_idle() will return true, which tells readers that
+ * they can once again use their fastpaths.
+ */
+void rcu_sync_exit(struct rcu_sync *rsp)
+{
+ spin_lock_irq(&rsp->rss_lock);
+ if (!--rsp->gp_count) {
+ if (rsp->cb_state == CB_IDLE) {
+ rsp->cb_state = CB_PENDING;
+ gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
+ } else if (rsp->cb_state == CB_PENDING) {
+ rsp->cb_state = CB_REPLAY;
+ }
+ }
+ spin_unlock_irq(&rsp->rss_lock);
+}
+
+/**
+ * rcu_sync_dtor() - Clean up an rcu_sync structure
+ * @rsp: Pointer to rcu_sync structure to be cleaned up
+ */
+void rcu_sync_dtor(struct rcu_sync *rsp)
+{
+ int cb_state;
+
+ BUG_ON(rsp->gp_count);
+
+ spin_lock_irq(&rsp->rss_lock);
+ if (rsp->cb_state == CB_REPLAY)
+ rsp->cb_state = CB_PENDING;
+ cb_state = rsp->cb_state;
+ spin_unlock_irq(&rsp->rss_lock);
+
+ if (cb_state != CB_IDLE) {
+ gp_ops[rsp->gp_type].wait();
+ BUG_ON(rsp->cb_state != CB_IDLE);
+ }
+}
Code Review / kvmfornfv.git / blobdiff