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/init.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.  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  */
  70 void __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
  80 static 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  */
  92 static 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
  99 static int show_tiny_stats_open(struct inode *inode, struct file *file)
 100 {
 101         return single_open(file, show_tiny_stats, NULL);
 102 }
 103
 104 static 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
 112 static struct dentry *rcudir;
 113
 114 static 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;
 126 free_out:
 127         debugfs_remove_recursive(rcudir);
 128         return 1;
 129 }
 130 device_initcall(rcutiny_trace_init);
 131
 132 static 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
 155 static 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
 163 static 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 */