linux/kernel/rcu/sync.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * RCU-based infrastructure for lightweight reader-writer locking
 *
 * Copyright (c) 2015, Red Hat, Inc.
 *
 * Author: Oleg Nesterov <[email protected]>
 */

#include <linux/rcu_sync.h>
#include <linux/sched.h>

enum { … };

#define rss_lock …

/**
 * rcu_sync_init() - Initialize an rcu_sync structure
 * @rsp: Pointer to rcu_sync structure to be initialized
 */
void rcu_sync_init(struct rcu_sync *rsp)
{ … }

static void rcu_sync_func(struct rcu_head *rhp);

static void rcu_sync_call(struct rcu_sync *rsp)
{ … }

/**
 * rcu_sync_func() - Callback function managing reader access to fastpath
 * @rhp: Pointer to rcu_head in rcu_sync structure to use for synchronization
 *
 * This function is passed to call_rcu() function by rcu_sync_enter() and
 * rcu_sync_exit(), so that it is invoked after a grace period following the
 * that invocation of enter/exit.
 *
 * If it is called by rcu_sync_enter() it signals that all the readers were
 * switched onto slow path.
 *
 * If it is called by 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 *rhp)
{ … }

/**
 * 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 fastpaths.
 *
 * 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)
{ … }

/**
 * rcu_sync_exit() - Allow readers back onto fast path 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)
{ … }

/**
 * 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)
{ … }