1/*
  2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
  3 * Internal non-public definitions that provide either classic
  4 * or preemptible semantics.
  5 *
  6 * This program is free software; you can redistribute it and/or modify
  7 * it under the terms of the GNU General Public License as published by
  8 * the Free Software Foundation; either version 2 of the License, or
  9 * (at your option) any later version.
 10 *
 11 * This program is distributed in the hope that it will be useful,
 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 14 * GNU General Public License for more details.
 15 *
 16 * You should have received a copy of the GNU General Public License
 17 * along with this program; if not, you can access it online at
 18 * http://www.gnu.org/licenses/gpl-2.0.html.
 19 *
 20 * Copyright (c) 2010 Linaro
 21 *
 22 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 23 */
 24
 25#include <linux/kthread.h>
 26#include <linux/init.h>
 27#include <linux/debugfs.h>
 28#include <linux/seq_file.h>
 29
 30/* Global control variables for rcupdate callback mechanism. */
 31struct rcu_ctrlblk {
 32	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
 33	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
 34	struct rcu_head **curtail;	/* ->next pointer of last CB. */
 35	RCU_TRACE(long qlen);		/* Number of pending CBs. */
 36	RCU_TRACE(unsigned long gp_start); /* Start time for stalls. */
 37	RCU_TRACE(unsigned long ticks_this_gp); /* Statistic for stalls. */
 38	RCU_TRACE(unsigned long jiffies_stall); /* Jiffies at next stall. */
 39	RCU_TRACE(const char *name);	/* Name of RCU type. */
 40};
 41
 42/* Definition for rcupdate control block. */
 43static struct rcu_ctrlblk rcu_sched_ctrlblk = {
 44	.donetail	= &rcu_sched_ctrlblk.rcucblist,
 45	.curtail	= &rcu_sched_ctrlblk.rcucblist,
 46	RCU_TRACE(.name = "rcu_sched")
 47};
 48
 49static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 50	.donetail	= &rcu_bh_ctrlblk.rcucblist,
 51	.curtail	= &rcu_bh_ctrlblk.rcucblist,
 52	RCU_TRACE(.name = "rcu_bh")
 53};
 54
 55#ifdef CONFIG_DEBUG_LOCK_ALLOC
 56#include <linux/kernel_stat.h>
 57
 58int rcu_scheduler_active __read_mostly;
 59EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 60
 61/*
 62 * During boot, we forgive RCU lockdep issues.  After this function is
 63 * invoked, we start taking RCU lockdep issues seriously.  Note that unlike
 64 * Tree RCU, Tiny RCU transitions directly from RCU_SCHEDULER_INACTIVE
 65 * to RCU_SCHEDULER_RUNNING, skipping the RCU_SCHEDULER_INIT stage.
 66 * The reason for this is that Tiny RCU does not need kthreads, so does
 67 * not have to care about the fact that the scheduler is half-initialized
 68 * at a certain phase of the boot process.
 69 */
 70void __init rcu_scheduler_starting(void)
 71{
 72	WARN_ON(nr_context_switches() > 0);
 73	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
 74}
 75
 76#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 77
 78#ifdef CONFIG_RCU_TRACE
 79
 80static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
 81{
 82	unsigned long flags;
 83
 84	local_irq_save(flags);
 85	rcp->qlen -= n;
 86	local_irq_restore(flags);
 87}
 88
 89/*
 90 * Dump statistics for TINY_RCU, such as they are.
 91 */
 92static int show_tiny_stats(struct seq_file *m, void *unused)
 93{
 94	seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
 95	seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
 96	return 0;
 97}
 98
 99static int show_tiny_stats_open(struct inode *inode, struct file *file)
100{
101	return single_open(file, show_tiny_stats, NULL);
102}
103
104static const struct file_operations show_tiny_stats_fops = {
105	.owner = THIS_MODULE,
106	.open = show_tiny_stats_open,
107	.read = seq_read,
108	.llseek = seq_lseek,
109	.release = single_release,
110};
111
112static struct dentry *rcudir;
113
114static int __init rcutiny_trace_init(void)
115{
116	struct dentry *retval;
117
118	rcudir = debugfs_create_dir("rcu", NULL);
119	if (!rcudir)
120		goto free_out;
121	retval = debugfs_create_file("rcudata", 0444, rcudir,
122				     NULL, &show_tiny_stats_fops);
123	if (!retval)
124		goto free_out;
125	return 0;
126free_out:
127	debugfs_remove_recursive(rcudir);
128	return 1;
129}
130device_initcall(rcutiny_trace_init);
131
132static void check_cpu_stall(struct rcu_ctrlblk *rcp)
133{
134	unsigned long j;
135	unsigned long js;
136
137	if (rcu_cpu_stall_suppress)
138		return;
139	rcp->ticks_this_gp++;
140	j = jiffies;
141	js = READ_ONCE(rcp->jiffies_stall);
142	if (rcp->rcucblist && ULONG_CMP_GE(j, js)) {
143		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
144		       rcp->name, rcp->ticks_this_gp, DYNTICK_TASK_EXIT_IDLE,
145		       jiffies - rcp->gp_start, rcp->qlen);
146		dump_stack();
147		WRITE_ONCE(rcp->jiffies_stall,
148			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
149	} else if (ULONG_CMP_GE(j, js)) {
150		WRITE_ONCE(rcp->jiffies_stall,
151			   jiffies + rcu_jiffies_till_stall_check());
152	}
153}
154
155static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
156{
157	rcp->ticks_this_gp = 0;
158	rcp->gp_start = jiffies;
159	WRITE_ONCE(rcp->jiffies_stall,
160		   jiffies + rcu_jiffies_till_stall_check());
161}
162
163static void check_cpu_stalls(void)
164{
165	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
166	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
167}
168
169#endif /* #ifdef CONFIG_RCU_TRACE */