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/module.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.
64 */
65void __init rcu_scheduler_starting(void)
66{
67	WARN_ON(nr_context_switches() > 0);
68	rcu_scheduler_active = 1;
69}
70
71#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
72
73#ifdef CONFIG_RCU_TRACE
74
75static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
76{
77	unsigned long flags;
78
79	local_irq_save(flags);
80	rcp->qlen -= n;
81	local_irq_restore(flags);
82}
83
84/*
85 * Dump statistics for TINY_RCU, such as they are.
86 */
87static int show_tiny_stats(struct seq_file *m, void *unused)
88{
89	seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
90	seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
91	return 0;
92}
93
94static int show_tiny_stats_open(struct inode *inode, struct file *file)
95{
96	return single_open(file, show_tiny_stats, NULL);
97}
98
99static const struct file_operations show_tiny_stats_fops = {
100	.owner = THIS_MODULE,
101	.open = show_tiny_stats_open,
102	.read = seq_read,
103	.llseek = seq_lseek,
104	.release = single_release,
105};
106
107static struct dentry *rcudir;
108
109static int __init rcutiny_trace_init(void)
110{
111	struct dentry *retval;
112
113	rcudir = debugfs_create_dir("rcu", NULL);
114	if (!rcudir)
115		goto free_out;
116	retval = debugfs_create_file("rcudata", 0444, rcudir,
117				     NULL, &show_tiny_stats_fops);
118	if (!retval)
119		goto free_out;
120	return 0;
121free_out:
122	debugfs_remove_recursive(rcudir);
123	return 1;
124}
125
126static void __exit rcutiny_trace_cleanup(void)
127{
128	debugfs_remove_recursive(rcudir);
129}
130
131module_init(rcutiny_trace_init);
132module_exit(rcutiny_trace_cleanup);
133
134MODULE_AUTHOR("Paul E. McKenney");
135MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
136MODULE_LICENSE("GPL");
137
138static void check_cpu_stall(struct rcu_ctrlblk *rcp)
139{
140	unsigned long j;
141	unsigned long js;
142
143	if (rcu_cpu_stall_suppress)
144		return;
145	rcp->ticks_this_gp++;
146	j = jiffies;
147	js = ACCESS_ONCE(rcp->jiffies_stall);
148	if (rcp->rcucblist && ULONG_CMP_GE(j, js)) {
149		pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
150		       rcp->name, rcp->ticks_this_gp, DYNTICK_TASK_EXIT_IDLE,
151		       jiffies - rcp->gp_start, rcp->qlen);
152		dump_stack();
153		ACCESS_ONCE(rcp->jiffies_stall) = jiffies +
154			3 * rcu_jiffies_till_stall_check() + 3;
155	} else if (ULONG_CMP_GE(j, js)) {
156		ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
157	}
158}
159
160static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
161{
162	rcp->ticks_this_gp = 0;
163	rcp->gp_start = jiffies;
164	ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
165}
166
167static void check_cpu_stalls(void)
168{
169	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
170	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
171}
172
173#endif /* #ifdef CONFIG_RCU_TRACE */
174