LXR linux/kernel/rcu/tiny

   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.
  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}
 125device_initcall(rcutiny_trace_init);
 126
 127static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 128{
 129        unsigned long j;
 130        unsigned long js;
 131
 132        if (rcu_cpu_stall_suppress)
 133                return;
 134        rcp->ticks_this_gp++;
 135        j = jiffies;
 136        js = READ_ONCE(rcp->jiffies_stall);
 137        if (rcp->rcucblist && ULONG_CMP_GE(j, js)) {
 138                pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
 139                       rcp->name, rcp->ticks_this_gp, DYNTICK_TASK_EXIT_IDLE,
 140                       jiffies - rcp->gp_start, rcp->qlen);
 141                dump_stack();
 142                WRITE_ONCE(rcp->jiffies_stall,
 143                           jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 144        } else if (ULONG_CMP_GE(j, js)) {
 145                WRITE_ONCE(rcp->jiffies_stall,
 146                           jiffies + rcu_jiffies_till_stall_check());
 147        }
 148}
 149
 150static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 151{
 152        rcp->ticks_this_gp = 0;
 153        rcp->gp_start = jiffies;
 154        WRITE_ONCE(rcp->jiffies_stall,
 155                   jiffies + rcu_jiffies_till_stall_check());
 156}
 157
 158static void check_cpu_stalls(void)
 159{
 160        RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
 161        RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
 162}
 163
 164#endif /* #ifdef CONFIG_RCU_TRACE */
 165