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.  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 */
 170