kernel/rcu/tiny_plugin.h

   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. */
  31 struct 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. */
  43 static 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
  49 static 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
  58 int rcu_scheduler_active __read_mostly;
  59 EXPORT_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  */
  65 void __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
  75 static 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  */
  87 static 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
  94 static int show_tiny_stats_open(struct inode *inode, struct file *file)
  95 {
  96         return single_open(file, show_tiny_stats, NULL);
  97 }
  98
  99 static 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
 107 static struct dentry *rcudir;
 108
 109 static 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;
 121 free_out:
 122         debugfs_remove_recursive(rcudir);
 123         return 1;
 124 }
 125
 126 static void __exit rcutiny_trace_cleanup(void)
 127 {
 128         debugfs_remove_recursive(rcudir);
 129 }
 130
 131 module_init(rcutiny_trace_init);
 132 module_exit(rcutiny_trace_cleanup);
 133
 134 MODULE_AUTHOR("Paul E. McKenney");
 135 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
 136 MODULE_LICENSE("GPL");
 137
 138 static 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->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                 ACCESS_ONCE(rcp->jiffies_stall) = jiffies +
 156                         3 * rcu_jiffies_till_stall_check() + 3;
 157         else if (ULONG_CMP_GE(j, js))
 158                 ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
 159 }
 160
 161 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 162 {
 163         rcp->ticks_this_gp = 0;
 164         rcp->gp_start = jiffies;
 165         ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
 166 }
 167
 168 static 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 */