LXR linux/kernel/rcutiny

   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, write to the Free Software
  18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  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(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 = rcp->jiffies_stall;
 148        if (*rcp->curtail && 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, rcu_dynticks_nesting,
 151                       jiffies - rcp->gp_start, rcp->qlen);
 152                dump_stack();
 153        }
 154        if (*rcp->curtail && ULONG_CMP_GE(j, js))
 155                rcp->jiffies_stall = jiffies +
 156                        3 * rcu_jiffies_till_stall_check() + 3;
 157        else if (ULONG_CMP_GE(j, js))
 158                rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
 159}
 160
 161static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 162{
 163        rcp->ticks_this_gp = 0;
 164        rcp->gp_start = jiffies;
 165        rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
 166}
 167
 168static void check_cpu_stalls(void)
 169{
 170        RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
 171        RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
 172}
 173
 174#endif /* #ifdef CONFIG_RCU_TRACE */
 175