path: root/kernel/rcutiny_plugin.h

/*
 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
 * Internal non-public definitions that provide either classic
 * or preemptible semantics.
 *
 * 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (c) 2010 Linaro
 *
 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 */

#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>

/* Global control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
	struct rcu_head **curtail;	/* ->next pointer of last CB. */
	RCU_TRACE(long qlen);		/* Number of pending CBs. */
	RCU_TRACE(char *name);		/* Name of RCU type. */
};

/* Definition for rcupdate control block. */
static struct rcu_ctrlblk rcu_sched_ctrlblk = {
	.donetail	= &rcu_sched_ctrlblk.rcucblist,
	.curtail	= &rcu_sched_ctrlblk.rcucblist,
	RCU_TRACE(.name = "rcu_sched")
};

static struct rcu_ctrlblk rcu_bh_ctrlblk = {
	.donetail	= &rcu_bh_ctrlblk.rcucblist,
	.curtail	= &rcu_bh_ctrlblk.rcucblist,
	RCU_TRACE(.name = "rcu_bh")
};

#ifdef CONFIG_DEBUG_LOCK_ALLOC
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

#ifdef CONFIG_TINY_PREEMPT_RCU

#include <linux/delay.h>

/* Global control variables for preemptible RCU. */
struct rcu_preempt_ctrlblk {
	struct rcu_ctrlblk rcb;	/* curtail: ->next ptr of last CB for GP. */
	struct rcu_head **nexttail;
				/* Tasks blocked in a preemptible RCU */
				/*  read-side critical section while an */
				/*  preemptible-RCU grace period is in */
				/*  progress must wait for a later grace */
				/*  period.  This pointer points to the */
				/*  ->next pointer of the last task that */
				/*  must wait for a later grace period, or */
				/*  to &->rcb.rcucblist if there is no */
				/*  such task. */
	struct list_head blkd_tasks;
				/* Tasks blocked in RCU read-side critical */
				/*  section.  Tasks are placed at the head */
				/*  of this list and age towards the tail. */
	struct list_head *gp_tasks;
				/* Pointer to the first task blocking the */
				/*  current grace period, or NULL if there */
				/*  is no such task. */
	struct list_head *exp_tasks;
				/* Pointer to first task blocking the */
				/*  current expedited grace period, or NULL */
				/*  if there is no such task.  If there */
				/*  is no current expedited grace period, */
				/*  then there cannot be any such task. */
#ifdef CONFIG_RCU_BOOST
	struct list_head *boost_tasks;
				/* Pointer to first task that needs to be */
				/*  priority-boosted, or NULL if no priority */
				/*  boosting is needed.  If there is no */
				/*  current or expedited grace period, there */
				/*  can be no such task. */
#endif /* #ifdef CONFIG_RCU_BOOST */
	u8 gpnum;		/* Current grace period. */
	u8 gpcpu;		/* Last grace period blocked by the CPU. */
	u8 completed;		/* Last grace period completed. */
				/*  If all three are equal, RCU is idle. */
#ifdef CONFIG_RCU_BOOST
	unsigned long boost_time; /* When to start boosting (jiffies) */
#endif /* #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_RCU_TRACE
	unsigned long n_grace_periods;
#ifdef CONFIG_RCU_BOOST
	unsigned long n_tasks_boosted;
				/* Total number of tasks boosted. */
	unsigned long n_exp_boosts;
				/* Number of tasks boosted for expedited GP. */
	unsigned long n_normal_boosts;
				/* Number of tasks boosted for normal GP. */
	unsigned long n_balk_blkd_tasks;
				/* Refused to boost: no blocked tasks. */
	unsigned long n_balk_exp_gp_tasks;
				/* Refused to boost: nothing blocking GP. */
	unsigned long n_balk_boost_tasks;
				/* Refused to boost: already boosting. */
	unsigned long n_balk_notyet;
				/* Refused to boost: not yet time. */
	unsigned long n_balk_nos;
				/* Refused to boost: not sure why, though. */
				/*  This can happen due to race conditions. */
#endif /* #ifdef CONFIG_RCU_BOOST */
#endif /* #ifdef CONFIG_RCU_TRACE */
};

static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
	.rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
	.rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
	.nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
	.blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
	RCU_TRACE(.rcb.name = "rcu_preempt")
};

static void rcu_read_unlock_special(struct task_struct *t);
static int rcu_preempted_readers_exp(void);
static void rcu_report_exp_done(void);

/*
 * Return true if the CPU has not yet responded to the current grace period.
 */
static int rcu_cpu_blocking_cur_gp(void)
{
	return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
}

/*
 * Check for a running RCU reader.  Because there is only one CPU,
 * there can be but one running RCU reader at a time.  ;-)
 *
 * Returns zero if there are no running readers.  Returns a positive
 * number if there is at least one reader within its RCU read-side
 * critical section.  Returns a negative number if an outermost reader
 * is in the midst o