kernel/rcutiny_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, 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. */
  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(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 int rcu_scheduler_active __read_mostly;
  57 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  58 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  59
  60 #ifdef CONFIG_RCU_TRACE
  61
  62 static void check_cpu_stall(struct rcu_ctrlblk *rcp)
  63 {
  64         unsigned long j;
  65         unsigned long js;
  66
  67         if (rcu_cpu_stall_suppress)
  68                 return;
  69         rcp->ticks_this_gp++;
  70         j = jiffies;
  71         js = rcp->jiffies_stall;
  72         if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
  73                 pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
  74                        rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
  75                        jiffies - rcp->gp_start, rcp->qlen);
  76                 dump_stack();
  77         }
  78         if (*rcp->curtail && ULONG_CMP_GE(j, js))
  79                 rcp->jiffies_stall = jiffies +
  80                         3 * rcu_jiffies_till_stall_check() + 3;
  81         else if (ULONG_CMP_GE(j, js))
  82                 rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
  83 }
  84
  85 static void check_cpu_stall_preempt(void);
  86
  87 #endif /* #ifdef CONFIG_RCU_TRACE */
  88
  89 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
  90 {
  91 #ifdef CONFIG_RCU_TRACE
  92         rcp->ticks_this_gp = 0;
  93         rcp->gp_start = jiffies;
  94         rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
  95 #endif /* #ifdef CONFIG_RCU_TRACE */
  96 }
  97
  98 static void check_cpu_stalls(void)
  99 {
 100         RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
 101         RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
 102         RCU_TRACE(check_cpu_stall_preempt());
 103 }
 104
 105 /*
 106  * Because preemptible RCU does not exist, it never has any callbacks
 107  * to process.
 108  */
 109 static void rcu_preempt_process_callbacks(void)
 110 {
 111 }
 112
 113 /* Hold off callback invocation until early_initcall() time. */
 114 static int rcu_scheduler_fully_active __read_mostly;
 115
 116 /*
 117  * Start up softirq processing of callbacks.
 118  */
 119 void invoke_rcu_callbacks(void)
 120 {
 121         if (rcu_scheduler_fully_active)
 122                 raise_softirq(RCU_SOFTIRQ);
 123 }
 124
 125 #ifdef CONFIG_RCU_TRACE
 126
 127 /*
 128  * There is no callback kthread, so this thread is never it.
 129  */
 130 static bool rcu_is_callbacks_kthread(void)
 131 {
 132         return false;
 133 }
 134
 135 #endif /* #ifdef CONFIG_RCU_TRACE */
 136
 137 static int __init rcu_scheduler_really_started(void)
 138 {
 139         rcu_scheduler_fully_active = 1;
 140         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 141         raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
 142         return 0;
 143 }
 144 early_initcall(rcu_scheduler_really_started);
 145
 146 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 147 #include <linux/kernel_stat.h>
 148
 149 /*
 150  * During boot, we forgive RCU lockdep issues.  After this function is
 151  * invoked, we start taking RCU lockdep issues seriously.
 152  */
 153 void __init rcu_scheduler_starting(void)
 154 {
 155         WARN_ON(nr_context_switches() > 0);
 156         rcu_scheduler_active = 1;
 157 }
 158
 159 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 160
 161 #ifdef CONFIG_RCU_TRACE
 162
 163 static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
 164 {
 165         unsigned long flags;
 166
 167         local_irq_save(flags);
 168         rcp->qlen -= n;
 169         local_irq_restore(flags);
 170 }
 171
 172 /*
 173  * Dump statistics for TINY_RCU, such as they are.
 174  */
 175 static int show_tiny_stats(struct seq_file *m, void *unused)
 176 {
 177         seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
 178         seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
 179         return 0;
 180 }
 181
 182 static int show_tiny_stats_open(struct inode *inode, struct file *file)
 183 {
 184         return single_open(file, show_tiny_stats, NULL);
 185 }
 186
 187 static const struct file_operations show_tiny_stats_fops = {
 188         .owner = THIS_MODULE,
 189         .open = show_tiny_stats_open,
 190         .read = seq_read,
 191         .llseek = seq_lseek,
 192         .release = single_release,
 193 };
 194
 195 static struct dentry *rcudir;
 196
 197 static int __init rcutiny_trace_init(void)
 198 {
 199         struct dentry *retval;
 200
 201         rcudir = debugfs_create_dir("rcu", NULL);
 202         if (!rcudir)
 203                 goto free_out;
 204         retval = debugfs_create_file("rcudata", 0444, rcudir,
 205                                      NULL, &show_tiny_stats_fops);
 206         if (!retval)
 207                 goto free_out;
 208         return 0;
 209 free_out:
 210         debugfs_remove_recursive(rcudir);
 211         return 1;
 212 }
 213
 214 static void __exit rcutiny_trace_cleanup(void)
 215 {
 216         debugfs_remove_recursive(rcudir);
 217 }
 218
 219 module_init(rcutiny_trace_init);
 220 module_exit(rcutiny_trace_cleanup);
 221
 222 MODULE_AUTHOR("Paul E. McKenney");
 223 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
 224 MODULE_LICENSE("GPL");
 225
 226 static void check_cpu_stall_preempt(void)
 227 {
 228 }
 229
 230 #endif /* #ifdef CONFIG_RCU_TRACE */